/* ============================================================
   PySpark Interview Guide — Master Stylesheet
   ============================================================ */

/* ---------- CSS Custom Properties (Light Mode Default) ---------- */
:root {
  /* Primary palette */
  --color-primary:          #2563eb;
  --color-primary-hover:    #1d4ed8;
  --color-primary-light:    #dbeafe;
  --color-primary-dark:     #1e40af;
  --color-accent:           #7c3aed;
  --color-accent-light:     #ede9fe;

  /* Neutrals */
  --color-bg:               #ffffff;
  --color-bg-secondary:     #f8fafc;
  --color-bg-tertiary:      #f1f5f9;
  --color-surface:          #ffffff;
  --color-surface-hover:    #f1f5f9;
  --color-border:           #e2e8f0;
  --color-border-light:     #f1f5f9;

  /* Text */
  --color-text:             #0f172a;
  --color-text-secondary:   #475569;
  --color-text-tertiary:    #94a3b8;
  --color-text-inverse:     #ffffff;
  --color-heading:          #0f172a;

  /* Semantic */
  --color-success:          #16a34a;
  --color-success-dark:     #15803d;
  --color-success-bg:       #f0fdf4;
  --color-success-border:   #bbf7d0;
  --color-warning:          #d97706;
  --color-warning-bg:       #fffbeb;
  --color-warning-border:   #fde68a;
  --color-danger:           #dc2626;
  --color-danger-bg:        #fef2f2;
  --color-danger-border:    #fecaca;
  --color-info:             #2563eb;
  --color-info-bg:          #eff6ff;
  --color-info-border:      #bfdbfe;

  /* Code */
  --color-code-bg:          #1e293b;
  --color-code-text:        #e2e8f0;
  --color-code-keyword:     #c084fc;
  --color-code-string:      #86efac;
  --color-code-comment:     #64748b;
  --color-code-function:    #67e8f9;
  --color-code-number:      #fbbf24;
  --color-code-operator:    #f472b6;

  /* Layout */
  --nav-height:             64px;
  --sidebar-width:          280px;
  --content-max-width:      900px;

  /* Shadows */
  --shadow-sm:              0 1px 2px rgba(0,0,0,.05);
  --shadow-md:              0 4px 6px -1px rgba(0,0,0,.07), 0 2px 4px -2px rgba(0,0,0,.05);
  --shadow-lg:              0 10px 15px -3px rgba(0,0,0,.08), 0 4px 6px -4px rgba(0,0,0,.04);
  --shadow-xl:              0 20px 25px -5px rgba(0,0,0,.1), 0 8px 10px -6px rgba(0,0,0,.04);

  /* Radius */
  --radius-sm:              4px;
  --radius-md:              8px;
  --radius-lg:              12px;
  --radius-xl:              16px;
  --radius-full:            9999px;

  /* Transitions */
  --transition-fast:        150ms ease;
  --transition-base:        250ms ease;
  --transition-slow:        350ms ease;

  /* Z-index layers */
  --z-sidebar:              100;
  --z-nav:                  200;
  --z-overlay:              300;
  --z-modal:                400;
  --z-toast:                500;
}

/* ---------- Dark Mode ---------- */
[data-theme="dark"] {
  --color-primary:          #60a5fa;
  --color-primary-hover:    #93bbfd;
  --color-primary-light:    #1e3a5f;
  --color-primary-dark:     #3b82f6;
  --color-accent:           #a78bfa;
  --color-accent-light:     #2e1065;

  --color-bg:               #0f172a;
  --color-bg-secondary:     #1e293b;
  --color-bg-tertiary:      #334155;
  --color-surface:          #1e293b;
  --color-surface-hover:    #334155;
  --color-border:           #334155;
  --color-border-light:     #1e293b;

  --color-text:             #e2e8f0;
  --color-text-secondary:   #94a3b8;
  --color-text-tertiary:    #64748b;
  --color-text-inverse:     #0f172a;
  --color-heading:          #f1f5f9;

  --color-success-bg:       #052e16;
  --color-success-dark:     #22c55e;
  --color-success-border:   #14532d;
  --color-warning-bg:       #451a03;
  --color-warning-border:   #713f12;
  --color-danger-bg:        #450a0a;
  --color-danger-border:    #7f1d1d;
  --color-info-bg:          #172554;
  --color-info-border:      #1e3a8a;

  --color-code-bg:          #020617;

  --shadow-sm:              0 1px 2px rgba(0,0,0,.3);
  --shadow-md:              0 4px 6px -1px rgba(0,0,0,.4), 0 2px 4px -2px rgba(0,0,0,.3);
  --shadow-lg:              0 10px 15px -3px rgba(0,0,0,.45), 0 4px 6px -4px rgba(0,0,0,.3);
  --shadow-xl:              0 20px 25px -5px rgba(0,0,0,.5), 0 8px 10px -6px rgba(0,0,0,.35);
}

/* ============================================================
   BASE RESET & TYPOGRAPHY
   ============================================================ */
*,
*::before,
*::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

html {
  font-size: 16px;
  scroll-behavior: smooth;
  -webkit-text-size-adjust: 100%;
}

body {
  font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
  font-size: 1rem;
  line-height: 1.6;
  color: var(--color-text);
  background-color: var(--color-bg);
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  overflow-x: hidden;
}

h1, h2, h3, h4, h5, h6 {
  font-weight: 700;
  line-height: 1.3;
  color: var(--color-heading);
  margin-bottom: .5em;
}

h1 { font-size: 2.25rem; }
h2 { font-size: 1.75rem; }
h3 { font-size: 1.375rem; }
h4 { font-size: 1.125rem; }
h5 { font-size: 1rem; }
h6 { font-size: .875rem; }

/* Fix anchor hidden behind fixed navbar (64px) — applies to all section targets */
.topic-section,
section[id],
div[id],
h2[id],
h3[id],
[id] {
  scroll-margin-top: calc(var(--nav-height) + 16px);
}

p { margin-bottom: 1rem; }

a {
  color: var(--color-primary);
  text-decoration: none;
  transition: color var(--transition-fast);
}

a:hover { color: var(--color-primary-hover); }

img { max-width: 100%; height: auto; display: block; }

ul, ol { padding-left: 1.5rem; margin-bottom: 1rem; }

code, kbd, samp {
  font-family: 'JetBrains Mono', 'Fira Code', 'Cascadia Code', Consolas, monospace;
  font-size: .875em;
}

p code, li code, td code {
  background: var(--color-bg-tertiary);
  color: var(--color-primary);
  padding: .125em .375em;
  border-radius: var(--radius-sm);
  font-size: .85em;
}

hr {
  border: none;
  border-top: 1px solid var(--color-border);
  margin: 2rem 0;
}

::selection {
  background: var(--color-primary);
  color: var(--color-text-inverse);
}

/* ============================================================
   SCROLLBAR STYLING
   ============================================================ */
::-webkit-scrollbar {
  width: 8px;
  height: 8px;
}

::-webkit-scrollbar-track {
  background: var(--color-bg-secondary);
}

::-webkit-scrollbar-thumb {
  background: var(--color-border);
  border-radius: var(--radius-full);
}

::-webkit-scrollbar-thumb:hover {
  background: var(--color-text-tertiary);
}

/* Firefox */
* {
  scrollbar-width: thin;
  scrollbar-color: var(--color-border) var(--color-bg-secondary);
}

/* ============================================================
   TOP NAVIGATION BAR
   ============================================================ */
.navbar {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  height: var(--nav-height);
  background: rgba(255, 255, 255, .85);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--color-border);
  display: flex;
  align-items: center;
  padding: 0 1.5rem;
  z-index: var(--z-nav);
  transition: background var(--transition-base);
}

[data-theme="dark"] .navbar {
  background: rgba(15, 23, 42, .85);
}

/* Alternative nav class names (used in some pages) */
.nav-brand {
  display: flex;
  align-items: center;
  gap: .75rem;
  font-weight: 700;
  font-size: 1.25rem;
  color: var(--color-heading);
  flex-shrink: 0;
  text-decoration: none;
}

.nav-links {
  display: flex;
  align-items: center;
  gap: .25rem;
  flex: 1;
  overflow-x: auto;
  scrollbar-width: none;
  -ms-overflow-style: none;
}

.nav-links::-webkit-scrollbar {
  display: none;
}

.nav-links a {
  display: inline-flex;
  align-items: center;
  padding: .5rem .75rem;
  font-size: .875rem;
  font-weight: 500;
  color: var(--color-text-secondary);
  text-decoration: none;
  border-radius: var(--radius-md);
  white-space: nowrap;
  transition: all var(--transition-fast);
}

.nav-links a:hover {
  color: var(--color-text);
  background: var(--color-surface-hover);
}

.nav-links a.active {
  color: var(--color-primary);
  background: var(--color-primary-light);
}

.nav-actions {
  display: flex;
  align-items: center;
  gap: .5rem;
  flex-shrink: 0;
}

.icon-btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 40px;
  height: 40px;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  background: var(--color-surface);
  color: var(--color-text-secondary);
  cursor: pointer;
  transition: all var(--transition-fast);
}

.icon-btn:hover {
  background: var(--color-surface-hover);
  color: var(--color-text);
  border-color: var(--color-text-tertiary);
}

.icon-btn.hamburger {
  display: none;
}

@media (max-width: 768px) {
  .icon-btn.hamburger {
    display: inline-flex;
  }
  .nav-links {
    display: none;
  }
}

.navbar__brand {
  display: flex;
  align-items: center;
  gap: .75rem;
  font-weight: 700;
  font-size: 1.25rem;
  color: var(--color-heading);
  flex-shrink: 0;
}

.navbar__brand img {
  height: 32px;
  width: auto;
}

.navbar__title {
  white-space: nowrap;
}

.navbar__spacer {
  flex: 1;
}

.navbar__actions {
  display: flex;
  align-items: center;
  gap: .5rem;
}

.navbar__btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: .375rem;
  height: 40px;
  padding: 0 .875rem;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  background: var(--color-surface);
  color: var(--color-text-secondary);
  font-size: .875rem;
  font-weight: 500;
  cursor: pointer;
  transition: all var(--transition-fast);
  white-space: nowrap;
}

.navbar__btn:hover {
  background: var(--color-surface-hover);
  color: var(--color-text);
  border-color: var(--color-text-tertiary);
}

.navbar__btn--primary {
  background: var(--color-primary);
  color: #fff;
  border-color: var(--color-primary);
}

.navbar__btn--primary:hover {
  background: var(--color-primary-hover);
  border-color: var(--color-primary-hover);
  color: #fff;
}

/* Theme toggle icon */
.theme-toggle {
  width: 40px;
  padding: 0;
}

.theme-toggle__icon {
  font-size: 1.125rem;
  line-height: 1;
}

/* ============================================================
   SIDEBAR TOGGLE (HAMBURGER) — mobile-first
   ============================================================ */
.hub-mobile {
  display: none;
}
.sidebar-toggle {
  display: none;
  align-items: center;
  justify-content: center;
  width: 40px;
  height: 40px;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  background: var(--color-surface);
  color: var(--color-text);
  cursor: pointer;
  font-size: 1.25rem;
  flex-shrink: 0;
  transition: all var(--transition-fast);
}

.sidebar-toggle:hover {
  background: var(--color-surface-hover);
}

/* Hamburger icon bars */
.hamburger {
  display: flex;
  flex-direction: column;
  gap: 4px;
  width: 18px;
}

.hamburger__bar {
  display: block;
  width: 100%;
  height: 2px;
  background: currentColor;
  border-radius: 2px;
  transition: transform var(--transition-base), opacity var(--transition-base);
}

/* Animate to X when sidebar is open */
.sidebar-toggle.is-active .hamburger__bar:nth-child(1) {
  transform: translateY(6px) rotate(45deg);
}

.sidebar-toggle.is-active .hamburger__bar:nth-child(2) {
  opacity: 0;
}

.sidebar-toggle.is-active .hamburger__bar:nth-child(3) {
  transform: translateY(-6px) rotate(-45deg);
}

/* ============================================================
   LEFT SIDEBAR
   ============================================================ */
.sidebar {
  position: fixed;
  top: var(--nav-height);
  left: 0;
  bottom: 0;
  width: var(--sidebar-width);
  background: var(--color-surface);
  border-right: 1px solid var(--color-border);
  overflow-y: auto;
  overflow-x: hidden;
  z-index: var(--z-sidebar);
  padding: 1.5rem 0;
  transition: transform var(--transition-base);
}

.sidebar__section {
  margin-bottom: .5rem;
}

/* Alternative sidebar content class */
.sidebar-content {
  padding: 1rem 0;
}

.sidebar-content h3 {
  padding: 0 1.25rem;
  font-size: .875rem;
  font-weight: 600;
  color: var(--color-heading);
  margin-bottom: .75rem;
}

.sidebar-content ul {
  list-style: none;
  padding: 0;
  margin: 0;
}

.sidebar-content ul li a {
  display: block;
  padding: .5rem 1.25rem;
  font-size: .875rem;
  color: var(--color-text-secondary);
  text-decoration: none;
  border-left: 3px solid transparent;
  transition: all var(--transition-fast);
}

.sidebar-content ul li a:hover {
  color: var(--color-text);
  background: var(--color-surface-hover);
}

.sidebar-content ul li a.active {
  color: var(--color-primary);
  border-left-color: var(--color-primary);
  background: var(--color-primary-light);
  font-weight: 500;
}

.sidebar-nav {
  padding: .75rem 0;
}

.sidebar__heading {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: .5rem 1.25rem;
  font-size: .75rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: .05em;
  color: var(--color-text-tertiary);
  cursor: pointer;
  user-select: none;
  transition: color var(--transition-fast);
}

.sidebar__heading:hover {
  color: var(--color-text-secondary);
}

.sidebar__heading-icon {
  font-size: .625rem;
  transition: transform var(--transition-fast);
}

.sidebar__section.is-collapsed .sidebar__heading-icon {
  transform: rotate(-90deg);
}

.sidebar__links {
  list-style: none;
  padding: 0;
  margin: 0;
  overflow: hidden;
  max-height: 5000px;
  transition: max-height var(--transition-slow);
}

.sidebar__section.is-collapsed .sidebar__links {
  max-height: 0;
}

.sidebar__link {
  display: flex;
  align-items: center;
  gap: .5rem;
  padding: .4375rem 1.25rem .4375rem 1.5rem;
  font-size: .875rem;
  color: var(--color-text-secondary);
  text-decoration: none;
  border-left: 3px solid transparent;
  transition: all var(--transition-fast);
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.sidebar__link:hover {
  color: var(--color-text);
  background: var(--color-surface-hover);
}

.sidebar__link.is-active {
  color: var(--color-primary);
  border-left-color: var(--color-primary);
  background: var(--color-primary-light);
  font-weight: 500;
}

.sidebar__link-icon {
  flex-shrink: 0;
  width: 1rem;
  text-align: center;
  font-size: .8rem;
}

/* Desktop sidebar - visible on larger screens */
.sidebar--desktop {
  position: fixed;
  top: var(--nav-height);
  right: 0;
  left: auto;
  bottom: 0;
  width: var(--sidebar-width);
  background: var(--color-surface);
  border-left: 1px solid var(--color-border);
  border-right: none;
  overflow-y: auto;
  overflow-x: hidden;
  z-index: var(--z-sidebar);
  padding: 1.5rem 0;
  transform: translateX(100%);
  transition: transform var(--transition-base);
}

.sidebar--desktop.is-open {
  transform: translateX(0);
}

@media (min-width: 1025px) {
  .sidebar--desktop {
    transform: translateX(0);
  }

  .main {
    margin-right: var(--sidebar-width);
    max-width: calc(100vw - var(--sidebar-width) * 2);
  }
}

/* Sidebar overlay for mobile */
.sidebar-overlay {
  display: none;
  position: fixed;
  inset: 0;
  background: rgba(0, 0, 0, .45);
  z-index: calc(var(--z-sidebar) - 1);
  opacity: 0;
  transition: opacity var(--transition-base);
}

.sidebar-overlay.is-visible {
  opacity: 1;
  visibility: visible;
}

/* ============================================================
   MAIN CONTENT AREA
   ============================================================ */
.main {
  margin-top: var(--nav-height);
  margin-left: var(--sidebar-width);
  min-height: calc(100vh - var(--nav-height));
  padding: 2.5rem 3rem 4rem;
  max-width: calc(100vw - var(--sidebar-width));
  transition: margin-left var(--transition-base);
  border-top: none;
  box-shadow: none;
}

/* Hide fixed progress line at top of .main (unwanted 4px bar) */
div.progress-bar[style*="position:fixed"],
.progress-indicator {
  display: none !important;
}

.main__content {
  max-width: var(--content-max-width);
  margin: 0 auto;
}

/* Main content with sidebar support (alternative class pattern) */
.main-content {
  margin-top: var(--nav-height);
  min-height: calc(100vh - var(--nav-height));
  padding: 2.5rem 3rem 4rem;
  transition: margin-left var(--transition-base);
}

.main-content.with-sidebar {
  margin-left: var(--sidebar-width);
  max-width: calc(100vw - var(--sidebar-width));
}

.main-content > * {
  max-width: var(--content-max-width);
  margin-left: auto;
  margin-right: auto;
}

/* ============================================================
   HERO SECTION
   ============================================================ */
.hero {
  position: relative;
  padding: 4rem 2.5rem;
  border-radius: var(--radius-xl);
  background: linear-gradient(135deg, #2563eb 0%, #7c3aed 50%, #a855f7 100%);
  color: #ffffff;
  overflow: hidden;
  margin-bottom: 3rem;
}

.hero::before {
  content: '';
  position: absolute;
  inset: 0;
  background:
    radial-gradient(circle at 20% 50%, rgba(255,255,255,.1) 0%, transparent 50%),
    radial-gradient(circle at 80% 20%, rgba(255,255,255,.08) 0%, transparent 40%);
  pointer-events: none;
}

.hero__badge {
  display: inline-flex;
  align-items: center;
  gap: .375rem;
  background: rgba(255,255,255,.15);
  backdrop-filter: blur(4px);
  border: 1px solid rgba(255,255,255,.2);
  border-radius: var(--radius-full);
  padding: .25rem .875rem;
  font-size: .8125rem;
  font-weight: 500;
  margin-bottom: 1rem;
}

.hero__title {
  font-size: 2.5rem;
  font-weight: 800;
  line-height: 1.15;
  margin-bottom: .75rem;
  color: #fff;
}

.hero__subtitle {
  font-size: 1.125rem;
  line-height: 1.6;
  opacity: .9;
  max-width: 600px;
  margin-bottom: 1.5rem;
}

.hero__actions {
  display: flex;
  flex-wrap: wrap;
  gap: .75rem;
}

.hero__btn {
  display: inline-flex;
  align-items: center;
  gap: .5rem;
  padding: .75rem 1.5rem;
  border-radius: var(--radius-md);
  font-size: .9375rem;
  font-weight: 600;
  cursor: pointer;
  transition: all var(--transition-fast);
  text-decoration: none;
  border: none;
}

.hero__btn--primary {
  background: #ffffff;
  color: #2563eb;
}

.hero__btn--primary:hover {
  background: #f1f5f9;
  transform: translateY(-1px);
  box-shadow: 0 4px 12px rgba(0,0,0,.15);
  color: #1d4ed8;
}

.hero__btn--secondary {
  background: rgba(255,255,255,.15);
  color: #ffffff;
  border: 1px solid rgba(255,255,255,.3);
}

.hero__btn--secondary:hover {
  background: rgba(255,255,255,.25);
  transform: translateY(-1px);
}

.hero__stats {
  display: flex;
  gap: 2rem;
  margin-top: 2rem;
  padding-top: 1.5rem;
  border-top: 1px solid rgba(255,255,255,.2);
}

.hero__stat {
  text-align: center;
}

.hero__stat-value {
  font-size: 1.5rem;
  font-weight: 700;
}

.hero__stat-label {
  font-size: .8125rem;
  opacity: .75;
  margin-top: .125rem;
}

/* ============================================================
   LEARNING PATH CARDS GRID
   ============================================================ */
.learning-paths {
  margin-bottom: 3rem;
}

.learning-paths__grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 1.5rem;
}

.learning-path-card {
  position: relative;
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: 1.5rem;
  cursor: pointer;
  transition: all var(--transition-base);
  text-decoration: none;
  color: inherit;
  display: flex;
  flex-direction: column;
}

.learning-path-card:hover {
  border-color: var(--color-primary);
  box-shadow: var(--shadow-lg);
  transform: translateY(-2px);
}

.learning-path-card__icon {
  width: 48px;
  height: 48px;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: var(--radius-md);
  font-size: 1.5rem;
  margin-bottom: 1rem;
  background: var(--color-primary-light);
  color: var(--color-primary);
}

.learning-path-card__title {
  font-size: 1.125rem;
  font-weight: 600;
  margin-bottom: .375rem;
}

.learning-path-card__description {
  font-size: .875rem;
  color: var(--color-text-secondary);
  line-height: 1.5;
  flex: 1;
  margin-bottom: 1rem;
}

.learning-path-card__meta {
  display: flex;
  align-items: center;
  gap: 1rem;
  font-size: .8125rem;
  color: var(--color-text-tertiary);
}

.learning-path-card__meta span {
  display: flex;
  align-items: center;
  gap: .25rem;
}

/* ============================================================
   CONCEPT CARDS
   ============================================================ */
.concept-cards {
  margin-bottom: 3rem;
}

.concept-cards__grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
  gap: 1.25rem;
}

.concept-card {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: 1.5rem;
  transition: all var(--transition-base);
  position: relative;
  overflow: hidden;
}

.concept-card::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 3px;
  background: linear-gradient(90deg, var(--color-primary), var(--color-accent));
  opacity: 0;
  transition: opacity var(--transition-base);
}

.concept-card:hover {
  border-color: var(--color-primary);
  box-shadow: var(--shadow-md);
  transform: translateY(-2px);
}

.concept-card:hover::before {
  opacity: 1;
}

.concept-card__header {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  margin-bottom: .75rem;
}

.concept-card__title {
  font-size: 1rem;
  font-weight: 600;
}

.concept-card__body {
  font-size: .875rem;
  color: var(--color-text-secondary);
  line-height: 1.6;
  margin-bottom: 1rem;
}

.concept-card__tags {
  display: flex;
  flex-wrap: wrap;
  gap: .375rem;
}

.concept-card__tag {
  font-size: .75rem;
  padding: .125rem .5rem;
  border-radius: var(--radius-full);
  background: var(--color-bg-tertiary);
  color: var(--color-text-secondary);
  font-weight: 500;
}

/* ============================================================
   CODE BLOCKS & SYNTAX HIGHLIGHTING
   ============================================================ */
.code-block {
  position: relative;
  margin: 1.5rem 0;
  border-radius: var(--radius-lg);
  overflow: hidden;
  background: var(--color-code-bg);
  border: 1px solid var(--color-border);
}

.code-block__header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: .5rem 1rem;
  background: rgba(0,0,0,.2);
  border-bottom: 1px solid rgba(255,255,255,.06);
}

.code-block__lang {
  font-size: .75rem;
  font-weight: 600;
  color: var(--color-text-tertiary);
  text-transform: uppercase;
  letter-spacing: .05em;
}

.code-block__filename {
  font-size: .8125rem;
  color: var(--color-text-tertiary);
  font-family: 'JetBrains Mono', monospace;
}

/* Copy button */
.code-block__copy {
  display: inline-flex;
  align-items: center;
  gap: .375rem;
  padding: .3rem .625rem;
  border: 1px solid rgba(255,255,255,.1);
  border-radius: var(--radius-sm);
  background: rgba(255,255,255,.06);
  color: var(--color-text-tertiary);
  font-size: .75rem;
  cursor: pointer;
  transition: all var(--transition-fast);
  font-family: inherit;
}

.code-block__copy:hover {
  background: rgba(255,255,255,.12);
  color: var(--color-text);
  border-color: rgba(255,255,255,.2);
}

.code-block__copy.is-copied {
  color: var(--color-success);
  border-color: rgba(22, 163, 74, .3);
}

/* JS-added copy button inside <pre> — keep away from code */
.copy-btn {
  position: absolute;
  top: 10px;
  right: 10px;
  display: inline-flex;
  align-items: center;
  gap: .375rem;
  padding: .3rem .625rem;
  border: 1px solid rgba(255,255,255,.15);
  border-radius: var(--radius-sm);
  background: rgba(30,41,59,.95);
  color: #e2e8f0;
  font-size: .75rem;
  font-family: inherit;
  cursor: pointer;
  z-index: 2;
  box-shadow: 0 2px 8px rgba(0,0,0,.25);
}
.copy-btn:hover { background: rgba(51,65,85,.95); color: #fff; }
.copy-btn.copied, .copy-btn.is-copied { background: var(--color-success); color: #fff; border-color: var(--color-success); }
.code-block pre:has(.copy-btn) { padding-top: 2.75rem; }

.code-block pre {
  margin: 0;
  padding: 1.25rem;
  overflow-x: auto;
  font-size: .875rem;
  line-height: 1.7;
  color: var(--color-code-text);
  font-family: 'JetBrains Mono', monospace;
}

.code-block code {
  font-family: inherit;
  font-size: inherit;
  background: none;
  color: inherit;
  padding: 0;
  border-radius: 0;
}

/* Syntax token colors */
.token-keyword,
.token-kw   { color: var(--color-code-keyword); }
.token-string,
.token-str  { color: var(--color-code-string); }
.token-comment,
.token-cmt  { color: var(--color-code-comment); font-style: italic; }
.token-function,
.token-fn   { color: var(--color-code-function); }
.token-number,
.token-num  { color: var(--color-code-number); }
.token-operator,
.token-op   { color: var(--color-code-operator); }
.token-class,
.token-cls  { color: #f472b6; }
.token-param { color: #fb923c; }
.token-builtin { color: #38bdf8; }
.token-punctuation { color: #94a3b8; }

/* ============================================================
   COMPARISON TABLES
   ============================================================ */
.table-wrapper {
  overflow-x: auto;
  margin: 1.5rem 0;
  border-radius: var(--radius-lg);
  border: 1px solid var(--color-border);
}

.comparison-table {
  width: 100%;
  border-collapse: collapse;
  font-size: .875rem;
}

.comparison-table th {
  background: var(--color-bg-secondary);
  font-weight: 600;
  text-align: left;
  padding: .75rem 1rem;
  border-bottom: 2px solid var(--color-border);
  white-space: nowrap;
  color: var(--color-heading);
}

.comparison-table td {
  padding: .75rem 1rem;
  border-bottom: 1px solid var(--color-border-light);
  vertical-align: top;
  color: var(--color-text);
}

.comparison-table tbody tr:last-child td {
  border-bottom: none;
}

.comparison-table tbody tr:hover {
  background: var(--color-surface-hover);
}

.comparison-table code {
  font-size: .8125rem;
}

/* ============================================================
   INTERACTIVE DIAGRAM CONTAINERS
   ============================================================ */
.diagram-container {
  margin: 2rem 0;
  padding: 2rem;
  background: var(--color-bg-secondary);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  overflow-x: auto;
  text-align: center;
}

.diagram-container__title {
  font-size: .875rem;
  font-weight: 600;
  color: var(--color-text-secondary);
  text-transform: uppercase;
  letter-spacing: .04em;
  margin-bottom: 1.5rem;
}

.diagram-container svg,
.diagram-container img {
  max-width: 100%;
  height: auto;
}

.diagram-container__legend {
  display: flex;
  justify-content: center;
  flex-wrap: wrap;
  gap: 1rem;
  margin-top: 1.5rem;
  font-size: .8125rem;
  color: var(--color-text-secondary);
}

.diagram-container__legend-item {
  display: flex;
  align-items: center;
  gap: .375rem;
}

.diagram-container__legend-dot {
  width: 10px;
  height: 10px;
  border-radius: 50%;
  flex-shrink: 0;
}

/* ============================================================
   SEARCH OVERLAY / MODAL
   ============================================================ */
.search-overlay {
  position: fixed;
  inset: 0;
  background: rgba(0, 0, 0, .5);
  backdrop-filter: blur(4px);
  z-index: var(--z-overlay);
  display: flex;
  align-items: flex-start;
  justify-content: center;
  padding-top: 10vh;
  opacity: 0;
  visibility: hidden;
  transition: opacity var(--transition-base), visibility var(--transition-base);
}

.search-overlay.is-open,
.search-overlay.active {
  opacity: 1;
  visibility: visible;
}

.search-modal {
  width: 100%;
  max-width: 640px;
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-xl);
  box-shadow: var(--shadow-xl);
  overflow: hidden;
  transform: translateY(-10px) scale(.98);
  transition: transform var(--transition-base);
}

.search-overlay.is-open .search-modal,
.search-overlay.active .search-modal,
.search-overlay.active .search-container {
  transform: translateY(0) scale(1);
}

/* Alternative search container class */
.search-container {
  width: 100%;
  max-width: 640px;
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-xl);
  box-shadow: var(--shadow-xl);
  overflow: hidden;
  transform: translateY(-10px) scale(.98);
  transition: transform var(--transition-base);
}

.search-overlay.is-active .search-container {
  transform: translateY(0) scale(1);
}

.search-container input {
  width: 100%;
  border: none;
  background: none;
  font-size: 1rem;
  color: var(--color-text);
  outline: none;
  font-family: inherit;
  padding: 1rem 1.25rem;
}

.search-container .search-close {
  background: none;
  border: none;
  font-size: 1.5rem;
  color: var(--color-text-tertiary);
  cursor: pointer;
  padding: 0 1rem;
}

.search-modal__input-wrapper {
  display: flex;
  align-items: center;
  gap: .75rem;
  padding: 1rem 1.25rem;
  border-bottom: 1px solid var(--color-border);
}

.search-modal__icon {
  color: var(--color-text-tertiary);
  font-size: 1.125rem;
  flex-shrink: 0;
}

.search-modal__input {
  flex: 1;
  border: none;
  background: none;
  font-size: 1rem;
  color: var(--color-text);
  outline: none;
  font-family: inherit;
}

.search-modal__input::placeholder {
  color: var(--color-text-tertiary);
}

.search-modal__shortcut {
  font-size: .75rem;
  padding: .125rem .375rem;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-sm);
  color: var(--color-text-tertiary);
  font-family: inherit;
}

.search-modal__results {
  max-height: 400px;
  overflow-y: auto;
  padding: .5rem;
}

.search-modal__result {
  display: block;
  padding: .75rem 1rem;
  border-radius: var(--radius-md);
  color: var(--color-text);
  text-decoration: none;
  transition: background var(--transition-fast);
}

.search-modal__result:hover,
.search-modal__result.is-focused {
  background: var(--color-surface-hover);
}

.search-modal__result-title {
  font-weight: 600;
  font-size: .9375rem;
  margin-bottom: .125rem;
}

.search-modal__result-path {
  font-size: .8125rem;
  color: var(--color-text-tertiary);
}

.search-modal__empty {
  padding: 2rem;
  text-align: center;
  color: var(--color-text-tertiary);
  font-size: .9375rem;
}

/* ============================================================
   PROGRESS BAR
   ============================================================ */
.progress-bar {
  margin: 1rem 0;
}

.progress-bar__label {
  display: flex;
  justify-content: space-between;
  font-size: .8125rem;
  font-weight: 500;
  color: var(--color-text-secondary);
  margin-bottom: .375rem;
}

.progress-bar__track {
  width: 100%;
  height: 8px;
  background: var(--color-bg-tertiary);
  border-radius: var(--radius-full);
  overflow: hidden;
}

.progress-bar__fill {
  height: 100%;
  background: linear-gradient(90deg, var(--color-primary), var(--color-accent));
  border-radius: var(--radius-full);
  transition: width var(--transition-slow);
  min-width: 0;
}

.progress-bar--sm .progress-bar__track {
  height: 4px;
}

.progress-bar--lg .progress-bar__track {
  height: 12px;
}

/* Alternative progress indicator class */
.progress-indicator {
  position: fixed;
  top: var(--nav-height);
  left: 0;
  right: 0;
  height: 4px;
  background: var(--color-bg-tertiary);
  z-index: 90;
}

.progress-indicator .progress-bar {
  height: 100%;
  margin: 0;
}

.progress-indicator .progress-bar__track {
  height: 100%;
  border-radius: 0;
}

.progress-indicator .progress-bar__fill {
  border-radius: 0;
}

/* ============================================================
   BOOKMARK BUTTON
   ============================================================ */
.bookmark-btn {
  display: inline-flex;
  align-items: center;
  gap: .375rem;
  padding: .375rem .75rem;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  background: var(--color-surface);
  color: var(--color-text-secondary);
  font-size: .8125rem;
  cursor: pointer;
  transition: all var(--transition-fast);
  font-family: inherit;
  font-weight: 500;
}

.bookmark-btn:hover {
  background: var(--color-surface-hover);
  color: var(--color-text);
  border-color: var(--color-text-tertiary);
}

.bookmark-btn.is-bookmarked {
  background: var(--color-warning-bg);
  color: var(--color-warning);
  border-color: var(--color-warning-border);
}

.bookmark-btn.is-bookmarked:hover {
  background: var(--color-warning-bg);
}

.bookmark-btn__icon {
  font-size: 1rem;
  line-height: 1;
  transition: transform var(--transition-fast);
}

.bookmark-btn:hover .bookmark-btn__icon {
  transform: scale(1.15);
}

.bookmark-btn.is-bookmarked .bookmark-btn__icon {
  transform: scale(1.1);
}

/* ============================================================
   TOPIC COMPLETE BUTTON
   ============================================================ */
.topic-complete-btn {
  display: inline-flex;
  align-items: center;
  gap: .5rem;
  padding: .5rem 1rem;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  background: var(--color-surface);
  color: var(--color-text-secondary);
  font-size: .875rem;
  font-weight: 500;
  cursor: pointer;
  transition: all var(--transition-fast);
}

.topic-complete-btn:hover {
  border-color: var(--color-success);
  color: var(--color-success);
  background: var(--color-success-bg);
}

.topic-complete-btn.is-completed {
  background: var(--color-success);
  color: #fff;
  border-color: var(--color-success);
}

.topic-complete-btn.is-completed:hover {
  background: var(--color-success-dark);
}

/* ============================================================
   INTERVIEW TIP CARDS (Yellow)
   ============================================================ */
.tip-card {
  position: relative;
  background: var(--color-warning-bg);
  border: 1px solid var(--color-warning-border);
  border-radius: var(--radius-lg);
  padding: 1.25rem 1.25rem 1.25rem 3.5rem;
  margin: 1.5rem 0;
}

.tip-card::before {
  content: '';
  position: absolute;
  left: 1.25rem;
  top: 1.25rem;
  width: 20px;
  height: 20px;
  background: var(--color-warning);
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 20 20' fill='%23fff'%3E%3Cpath fill-rule='evenodd' d='M18 10a8 8 0 11-16 0 8 8 0 0116 0zm-7-4a1 1 0 11-2 0 1 1 0 012 0zM9 9a1 1 0 000 2v3a1 1 0 001 1h1a1 1 0 100-2v-3a1 1 0 00-1-1H9z' clip-rule='evenodd'/%3E%3C/svg%3E");
  background-repeat: no-repeat;
  background-position: center;
  background-size: 14px;
}

.tip-card__title {
  font-size: .9375rem;
  font-weight: 600;
  color: var(--color-warning);
  margin-bottom: .375rem;
}

.tip-card__body {
  font-size: .875rem;
  color: var(--color-text);
  line-height: 1.6;
}

.tip-card__body code {
  background: rgba(217, 119, 6, .12);
  color: var(--color-warning);
}

/* ============================================================
   WARNING / PROBLEM CARDS (Red)
   ============================================================ */
.warning-card {
  position: relative;
  background: var(--color-danger-bg);
  border: 1px solid var(--color-danger-border);
  border-radius: var(--radius-lg);
  padding: 1.25rem 1.25rem 1.25rem 3.5rem;
  margin: 1.5rem 0;
}

.warning-card::before {
  content: '';
  position: absolute;
  left: 1.25rem;
  top: 1.25rem;
  width: 20px;
  height: 20px;
  background: var(--color-danger);
  border-radius: 50%;
  background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 20 20' fill='%23fff'%3E%3Cpath fill-rule='evenodd' d='M8.257 3.099c.765-1.36 2.722-1.36 3.486 0l5.58 9.92c.75 1.334-.213 2.98-1.742 2.98H4.42c-1.53 0-2.493-1.646-1.743-2.98l5.58-9.92zM11 13a1 1 0 11-2 0 1 1 0 012 0zm-1-8a1 1 0 00-1 1v3a1 1 0 002 0V6a1 1 0 00-1-1z' clip-rule='evenodd'/%3E%3C/svg%3E");
  background-repeat: no-repeat;
  background-position: center;
  background-size: 14px;
}

.warning-card__title {
  font-size: .9375rem;
  font-weight: 600;
  color: var(--color-danger);
  margin-bottom: .375rem;
}

.warning-card__body {
  font-size: .875rem;
  color: var(--color-text);
  line-height: 1.6;
}

.warning-card__body code {
  background: rgba(220, 38, 38, .1);
  color: var(--color-danger);
}

/* ============================================================
   SUCCESS CARDS (Green)
   ============================================================ */
.success-card {
  position: relative;
  background: var(--color-success-bg);
  border: 1px solid var(--color-success-border);
  border-radius: var(--radius-lg);
  padding: 1.25rem 1.25rem 1.25rem 3.5rem;
  margin: 1.5rem 0;
}

.success-card::before {
  content: '';
  position: absolute;
  left: 1.25rem;
  top: 1.25rem;
  width: 20px;
  height: 20px;
  background: var(--color-success);
  border-radius: 50%;
  background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 20 20' fill='%23fff'%3E%3Cpath fill-rule='evenodd' d='M10 18a8 8 0 100-16 8 8 0 000 16zm3.707-9.293a1 1 0 00-1.414-1.414L9 10.586 7.707 9.293a1 1 0 00-1.414 1.414l2 2a1 1 0 001.414 0l4-4z' clip-rule='evenodd'/%3E%3C/svg%3E");
  background-repeat: no-repeat;
  background-position: center;
  background-size: 14px;
}

.success-card__title {
  font-size: .9375rem;
  font-weight: 600;
  color: var(--color-success);
  margin-bottom: .375rem;
}

.success-card__body {
  font-size: .875rem;
  color: var(--color-text);
  line-height: 1.6;
}

.success-card__body code {
  background: rgba(22, 163, 74, .1);
  color: var(--color-success);
}

/* ============================================================
   EXPANDABLE / COLLAPSIBLE SECTIONS
   ============================================================ */
.collapse {
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  margin: 1rem 0;
  overflow: hidden;
}

.collapse__trigger {
  display: flex;
  align-items: center;
  justify-content: space-between;
  width: 100%;
  padding: 1rem 1.25rem;
  background: var(--color-surface);
  border: none;
  color: var(--color-text);
  font-size: .9375rem;
  font-weight: 600;
  cursor: pointer;
  text-align: left;
  font-family: inherit;
  transition: background var(--transition-fast);
}

.collapse__trigger:hover {
  background: var(--color-surface-hover);
}

.collapse__trigger-icon {
  font-size: .75rem;
  color: var(--color-text-tertiary);
  transition: transform var(--transition-base);
}

.collapse.is-open .collapse__trigger-icon {
  transform: rotate(180deg);
}

.collapse__content {
  max-height: 0;
  overflow: hidden;
  transition: max-height var(--transition-slow);
}

.collapse.is-open .collapse__content {
  max-height: 2000px;
}

.collapse__body {
  padding: 1rem 1.25rem;
  border-top: 1px solid var(--color-border-light);
  font-size: .9375rem;
  line-height: 1.7;
  color: var(--color-text-secondary);
}

.collapse__body p:last-child {
  margin-bottom: 0;
}

/* ============================================================
   BADGE COMPONENTS (Difficulty Levels)
   ============================================================ */
.badge {
  display: inline-flex;
  align-items: center;
  gap: .25rem;
  padding: .1875rem .625rem;
  border-radius: var(--radius-full);
  font-size: .75rem;
  font-weight: 600;
  line-height: 1.4;
  white-space: nowrap;
}

.badge--easy {
  background: var(--color-success-bg);
  color: var(--color-success);
  border: 1px solid var(--color-success-border);
}

.badge--intermediate {
  background: var(--color-warning-bg);
  color: var(--color-warning);
  border: 1px solid var(--color-warning-border);
}

.badge--advanced {
  background: var(--color-danger-bg);
  color: var(--color-danger);
  border: 1px solid var(--color-danger-border);
}

.badge--info {
  background: var(--color-info-bg);
  color: var(--color-info);
  border: 1px solid var(--color-info-border);
}

.badge__dot {
  width: 6px;
  height: 6px;
  border-radius: 50%;
  background: currentColor;
}

/* ============================================================
   FOOTER
   ============================================================ */
.footer {
  margin-top: 4rem;
  padding: 2.5rem 0;
  border-top: 1px solid var(--color-border);
  color: var(--color-text-tertiary);
  font-size: .875rem;
}

.footer__inner {
  max-width: var(--content-max-width);
  margin: 0 auto;
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
  align-items: center;
  gap: 1rem;
}

.footer__links {
  display: flex;
  gap: 1.5rem;
  list-style: none;
  padding: 0;
  margin: 0;
}

.footer__links a {
  color: var(--color-text-secondary);
  font-size: .875rem;
  transition: color var(--transition-fast);
}

.footer__links a:hover {
  color: var(--color-primary);
}

.footer__copyright {
  width: 100%;
  text-align: center;
  margin-top: 1rem;
  font-size: .8125rem;
  color: var(--color-text-tertiary);
}

/* ============================================================
   UTILITY CLASSES
   ============================================================ */
.visually-hidden {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

.text-center { text-align: center; }
.text-primary { color: var(--color-primary); }
.text-success { color: var(--color-success); }
.text-warning { color: var(--color-warning); }
.text-danger  { color: var(--color-danger); }
.text-muted   { color: var(--color-text-tertiary); }

.mt-0 { margin-top: 0; }
.mt-1 { margin-top: .5rem; }
.mt-2 { margin-top: 1rem; }
.mt-3 { margin-top: 1.5rem; }
.mt-4 { margin-top: 2rem; }
.mb-0 { margin-bottom: 0; }
.mb-1 { margin-bottom: .5rem; }
.mb-2 { margin-bottom: 1rem; }
.mb-3 { margin-bottom: 1.5rem; }
.mb-4 { margin-bottom: 2rem; }

/* ============================================================
   ANIMATIONS
   ============================================================ */
@keyframes fadeIn {
  from { opacity: 0; }
  to   { opacity: 1; }
}

@keyframes fadeInUp {
  from { opacity: 0; transform: translateY(12px); }
  to   { opacity: 1; transform: translateY(0); }
}

@keyframes fadeInDown {
  from { opacity: 0; transform: translateY(-12px); }
  to   { opacity: 1; transform: translateY(0); }
}

@keyframes scaleIn {
  from { opacity: 0; transform: scale(.95); }
  to   { opacity: 1; transform: scale(1); }
}

@keyframes slideInLeft {
  from { transform: translateX(-100%); }
  to   { transform: translateX(0); }
}

@keyframes pulse {
  0%, 100% { opacity: 1; }
  50%      { opacity: .5; }
}

.animate-fade-in      { animation: fadeIn var(--transition-base) both; }
.animate-fade-in-up   { animation: fadeInUp var(--transition-base) both; }
.animate-fade-in-down { animation: fadeInDown var(--transition-base) both; }
.animate-scale-in     { animation: scaleIn var(--transition-base) both; }
.animate-pulse        { animation: pulse 2s ease-in-out infinite; }

/* Staggered children animation */
.stagger-children > * {
  opacity: 0;
  animation: fadeInUp .4s ease both;
}

.stagger-children > *:nth-child(1)  { animation-delay: .05s; }
.stagger-children > *:nth-child(2)  { animation-delay: .10s; }
.stagger-children > *:nth-child(3)  { animation-delay: .15s; }
.stagger-children > *:nth-child(4)  { animation-delay: .20s; }
.stagger-children > *:nth-child(5)  { animation-delay: .25s; }
.stagger-children > *:nth-child(6)  { animation-delay: .30s; }
.stagger-children > *:nth-child(7)  { animation-delay: .35s; }
.stagger-children > *:nth-child(8)  { animation-delay: .40s; }
.stagger-children > *:nth-child(9)  { animation-delay: .45s; }
.stagger-children > *:nth-child(10) { animation-delay: .50s; }

/* ============================================================
   RESPONSIVE — Tablets (<= 1024px)
   ============================================================ */
@media (max-width: 1024px) {
  .main {
    padding: 2rem 2rem 3rem;
  }

  .hero {
    padding: 3rem 2rem;
  }

  .hero__title {
    font-size: 2rem;
  }

  .hero__stats {
    gap: 1.5rem;
  }

  .learning-paths__grid {
    grid-template-columns: repeat(auto-fill, minmax(250px, 1fr));
  }
}

/* ============================================================
   RESPONSIVE — Mobile (<= 768px)
   ============================================================ */
@media (max-width: 768px) {
  :root {
    --sidebar-width: 280px;
  }

  /* Show hamburger, hide desktop sidebar toggle */
  .sidebar-toggle {
    display: flex !important;
    visibility: visible !important;
    opacity: 1 !important;
  }
  .navbar__actions {
    display: flex !important;
    align-items: center;
    gap: .35rem;
    margin-left: auto;
  }
  #hamburger {
    display: flex !important;
    order: 1;
  }
  /* Hub button inside actions: hidden on desktop, visible on mobile as 2nd item */
  .hub-mobile {
    display: inline-flex !important;
    order: 2;
  }
  /* Existing Hub in pyspark index (inside actions) also order 2 on mobile */
  .navbar__actions > a[href="../index.html"].navbar__btn {
    order: 2;
  }
  #theme-toggle {
    order: 3;
  }
  .search-trigger {
    order: 4;
  }

  /* Navbar adjustments — hide top links on mobile, keep hamburger */
  .navbar {
    padding: 0 1rem;
    gap: .5rem;
  }

  .navbar__title {
    font-size: 1rem;
  }

  .navbar__btn span.btn-label {
    display: none;
  }

  .navbar__links {
    display: none !important;
  }

  /* Hide top nav link buttons on mobile — keep Hub/search/theme/hamburger */
  .navbar__actions a.navbar__btn:has(.btn-label) {
    display: none !important;
  }

  /* Hide progress bar in nav on mobile to avoid overflow */
  .progress-bar--sm,
  .progress-bar.progress-bar--sm {
    display: none !important;
  }

  /* --- MOBILE: leftside content hidden, hamburger reveals it --- */
  /* Hide desktop sidebar completely on mobile — content full width */
  #sidebar {
    display: none !important;
    transform: translateX(-100%) !important;
  }
  #sidebar.is-open {
    transform: translateX(-100%) !important;
  }
  /* Mobile drawer — hidden off-canvas until hamburger opens */
  #mobile-nav {
    display: block !important;
    transform: translateX(-100%) !important;
    z-index: var(--z-sidebar);
    box-shadow: var(--shadow-xl);
  }
  #mobile-nav.is-open {
    transform: translateX(0) !important;
  }
  .sidebar-overlay {
    display: block;
    opacity: 0;
    visibility: hidden;
    pointer-events: none;
  }
  .sidebar-overlay.is-visible {
    opacity: 1;
    visibility: visible;
    pointer-events: auto;
  }

  /* Mobile overlay navigation */
  .mobile-overlay {
    display: none;
    position: fixed;
    inset: 0;
    background: rgba(0, 0, 0, .45);
    z-index: 998;
  }

  .mobile-overlay.is-active {
    display: block;
  }

  .mobile-nav {
    position: fixed;
    top: 0;
    left: 0;
    bottom: 0;
    width: 280px;
    background: var(--color-surface);
    z-index: 999;
    transform: translateX(-100%);
    transition: transform var(--transition-base);
    overflow-y: auto;
    padding: 1.5rem;
  }

  .mobile-nav.is-active {
    transform: translateX(0);
  }

  .mobile-nav a {
    display: block;
    padding: .75rem 1rem;
    color: var(--color-text-secondary);
    text-decoration: none;
    font-size: .9375rem;
    font-weight: 500;
    border-radius: var(--radius-md);
    transition: all var(--transition-fast);
  }

  .mobile-nav a:hover {
    color: var(--color-text);
    background: var(--color-surface-hover);
  }

  .mobile-nav a.active {
    color: var(--color-primary);
    background: var(--color-primary-light);
  }

  /* Main content full width on mobile — override inline margin-left */
  .main,
  .main[style] {
    margin-left: 0 !important;
    max-width: 100% !important;
    padding: 1.5rem 1rem 3rem !important;
  }

  .main-content.with-sidebar,
  .main-content.with-sidebar[style] {
    margin-left: 0 !important;
    max-width: 100% !important;
    padding: 1.5rem 1rem 3rem !important;
  }

  /* Footer — override inline margin-left:var(--sidebar-width) */
  footer[style] {
    margin-left: 0 !important;
    padding: 1.5rem 1rem !important;
  }

  /* Progress bar was hidden, but if shown ensure it doesn't offset */
  div.progress-bar[style] {
    left: 0 !important;
    right: 0 !important;
  }

  /* Hero — override inline padding/font-size on mobile */
  .hero,
  .hero[style] {
    padding: 2rem 1.25rem !important;
    margin-bottom: 2rem;
    border-radius: var(--radius-lg);
  }

  .hero__title,
  .hero h1[style] {
    font-size: 1.625rem !important;
  }

  .hero__subtitle {
    font-size: 1rem;
  }

  .hero__stats {
    flex-direction: column;
    gap: .75rem;
    align-items: flex-start;
  }

  .hero__stat {
    text-align: left;
    display: flex;
    align-items: center;
    gap: .5rem;
  }

  /* Grids stack to single column — override inline grid styles */
  .learning-paths__grid,
  .concept-cards__grid,
  div[style*="grid-template-columns"] {
    grid-template-columns: 1fr !important;
  }

  /* Tables scroll horizontally (already handled by wrapper) */
  .table-wrapper {
    margin-left: -1rem;
    margin-right: -1rem;
    border-radius: 0;
    overflow-x: auto;
    -webkit-overflow-scrolling: touch;
  }

  .code-block {
    max-width: 100%;
    overflow-x: auto;
  }

  .code-block pre {
    font-size: .8125rem;
    padding: 1rem;
    overflow-x: auto;
  }

  .diagram-container {
    padding: 1rem;
    overflow-x: auto;
  }

  /* Footer stacks */
  .footer__inner {
    flex-direction: column;
    text-align: center;
  }

  .footer__links {
    justify-content: center;
    flex-wrap: wrap;
  }

  /* Collapse: tap target bigger */
  .collapse__trigger {
    padding: 1rem;
  }

  /* Tip/Warning/Success cards tighter padding */
  .tip-card,
  .warning-card,
  .success-card {
    padding-left: 3rem;
  }

  /* Typography adjustments */
  h1 { font-size: 1.75rem; }
  h2 { font-size: 1.375rem; }
  h3 { font-size: 1.125rem; }
}

/* ============================================================
   PRINT STYLES
   ============================================================ */
@media print {
  *,
  *::before,
  *::after {
    background: transparent !important;
    color: #000 !important;
    box-shadow: none !important;
    text-shadow: none !important;
  }

  body {
    font-size: 12pt;
    line-height: 1.5;
  }

  .navbar,
  .sidebar,
  .sidebar-overlay,
  .sidebar-toggle,
  .search-overlay,
  .theme-toggle,
  .code-block__copy,
  .bookmark-btn,
  .footer {
    display: none !important;
  }

  .main {
    margin: 0;
    padding: 0;
    max-width: 100%;
  }

  .hero {
    padding: 1.5rem;
    border: 1px solid #ccc;
    break-inside: avoid;
  }

  h1, h2, h3, h4, h5, h6 {
    break-after: avoid;
  }

  pre, .code-block, .table-wrapper, .diagram-container {
    break-inside: avoid;
    page-break-inside: avoid;
  }

  .code-block {
    border: 1px solid #ccc;
  }

  .code-block pre {
    background: #f5f5f5 !important;
    color: #000 !important;
  }

  a[href]::after {
    content: " (" attr(href) ")";
    font-size: .875em;
    color: #555;
  }

  .tip-card,
  .warning-card,
  .success-card {
    border: 1px solid #999;
    padding-left: 1.25rem;
  }

  .tip-card::before,
  .warning-card::before,
  .success-card::before {
    display: none;
  }

  .comparison-table th {
    border-bottom: 2px solid #000;
  }

  .comparison-table td {
    border-bottom: 1px solid #ccc;
  }
}

/* ============================================================
   ARCHITECTURE PAGE — INTERACTIVE DIAGRAMS
   ============================================================ */

/* Topic section styling */
.topic-section {
  margin-bottom: 3rem;
  padding-bottom: 2rem;
  border-bottom: 1px solid var(--color-border);
}

.topic-section:last-of-type {
  border-bottom: none;
}

.topic-section__header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 0.75rem;
}

.topic-section__actions {
  display: flex;
  gap: 0.5rem;
  align-items: center;
}

/* Alternative section header class */
.section-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: .75rem;
  margin-bottom: 1.5rem;
}

.section-header h2 {
  margin: 0;
  flex: 1;
}

.section-actions {
  display: flex;
  gap: .5rem;
  align-items: center;
}

.section-intro {
  font-size: 1.0625rem;
  color: var(--color-text-secondary);
  margin-bottom: 1.5rem;
  line-height: 1.7;
}

/* Badge variants */
.badge-easy {
  background: var(--color-success-bg);
  color: var(--color-success);
  border: 1px solid var(--color-success-border);
}

.badge-intermediate {
  background: var(--color-warning-bg);
  color: var(--color-warning);
  border: 1px solid var(--color-warning-border);
}

.badge-advanced {
  background: var(--color-danger-bg);
  color: var(--color-danger);
  border: 1px solid var(--color-danger-border);
}

/* Interactive diagram components */
.diagram-component {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: 0.75rem 1.25rem;
  background: var(--color-surface);
  border: 2px solid var(--color-primary);
  border-radius: var(--radius-md);
  font-weight: 600;
  font-size: 0.875rem;
  color: var(--color-primary);
  cursor: pointer;
  transition: all var(--transition-fast);
  text-align: center;
  min-width: 120px;
}

.diagram-component:hover {
  background: var(--color-primary-light);
  transform: translateY(-2px);
  box-shadow: var(--shadow-md);
}

.diagram-component.selected {
  background: var(--color-primary);
  color: #fff;
  border-color: var(--color-primary);
}

/* Architecture flow - vertical */
.arch-flow {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.5rem;
  padding: 1rem;
}

.arch-arrow {
  font-size: 1.5rem;
  color: var(--color-text-tertiary);
  line-height: 1;
}

/* Plan flow - horizontal */
.plan-flow,
.catalyst-flow,
.dag-flow,
.aqe-flow {
  display: flex;
  align-items: center;
  justify-content: center;
  flex-wrap: wrap;
  gap: 0.75rem;
  padding: 1rem;
}

.plan-arrow {
  font-size: 1.25rem;
  color: var(--color-text-tertiary);
  font-weight: bold;
}

/* Stages flow */
.stages-flow {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 1rem;
  padding: 1.5rem;
}

.stage-box {
  background: var(--color-bg-secondary);
  border: 2px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: 1.25rem;
  min-width: 300px;
}

.stage-box__title {
  font-weight: 700;
  font-size: 0.875rem;
  color: var(--color-primary);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: 0.75rem;
  text-align: center;
}

.stage-box__content {
  display: flex;
  align-items: center;
  justify-content: center;
  flex-wrap: wrap;
  gap: 0.5rem;
}

.stage-box__content .diagram-component {
  min-width: 80px;
  font-size: 0.8125rem;
  padding: 0.5rem 0.75rem;
}

.shuffle-marker {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.25rem;
}

.shuffle-marker__arrow {
  font-size: 1.25rem;
  color: var(--color-danger);
  font-weight: bold;
}

.shuffle-marker__label {
  font-weight: 700;
  font-size: 0.75rem;
  color: var(--color-danger);
  text-transform: uppercase;
  letter-spacing: 0.1em;
  padding: 0.25rem 0.75rem;
  background: var(--color-danger-bg);
  border: 1px solid var(--color-danger-border);
  border-radius: var(--radius-full);
}

/* Executor flow */
.executor-flow {
  display: flex;
  justify-content: center;
  padding: 1rem;
}

.executor-box {
  background: var(--color-bg-secondary);
  border: 2px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: 1.25rem;
  min-width: 280px;
}

.executor-box__title {
  font-weight: 700;
  font-size: 0.875rem;
  color: var(--color-accent);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: 0.75rem;
  text-align: center;
}

.executor-box__content {
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
}

.executor-box__content .diagram-component {
  width: 100%;
  min-width: unset;
  background: var(--color-surface);
  border-color: var(--color-accent);
  color: var(--color-accent);
}

.executor-box__content .diagram-component:hover,
.executor-box__content .diagram-component.selected {
  background: var(--color-accent);
  color: #fff;
  border-color: var(--color-accent);
}

/* Diagram explanation panels */
.diagram-explanation {
  display: none;
  position: relative;
  background: var(--color-info-bg);
  border: 1px solid var(--color-info-border);
  border-radius: var(--radius-lg);
  padding: 1.25rem 1.25rem 1.25rem 1.25rem;
  margin: 1rem 0;
  animation: fadeIn 0.2s ease;
}

.diagram-explanation.active {
  display: block;
}

.diagram-explanation h4 {
  font-size: 0.9375rem;
  font-weight: 600;
  color: var(--color-info);
  margin-bottom: 0.5rem;
  margin-top: 0;
}

.diagram-explanation p {
  font-size: 0.875rem;
  color: var(--color-text);
  line-height: 1.6;
  margin: 0;
}

.diagram-close {
  position: absolute;
  top: 0.75rem;
  right: 0.75rem;
  width: 24px;
  height: 24px;
  display: flex;
  align-items: center;
  justify-content: center;
  background: none;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-sm);
  color: var(--color-text-tertiary);
  font-size: 1rem;
  cursor: pointer;
  transition: all var(--transition-fast);
}

.diagram-close:hover {
  background: var(--color-surface-hover);
  color: var(--color-text);
}

/* Responsive adjustments for diagrams */
@media (max-width: 768px) {
  .plan-flow,
  .catalyst-flow,
  .dag-flow,
  .aqe-flow {
    flex-direction: column;
  }

  .plan-arrow {
    transform: rotate(90deg);
  }

  .stage-box {
    min-width: unset;
    width: 100%;
  }

  .stage-box__content {
    flex-direction: column;
  }

  .diagram-component {
    min-width: unset;
    width: 100%;
  }

  .topic-section__header {
    flex-direction: column;
    align-items: flex-start;
    gap: 0.75rem;
  }
}

/* ============================================================
   Problem Cards (Real-World Scenarios)
   ============================================================ */
.problem-card {
  border: 2px solid var(--color-danger-border);
  border-radius: var(--radius-md);
  margin-bottom: 2rem;
  background: var(--color-surface);
  overflow: hidden;
  transition: box-shadow var(--transition-normal);
}

.problem-card:hover {
  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.08);
}

.problem-card__header {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  padding: 1rem 1.25rem;
}

.problem-card__header--problem {
  background: var(--color-danger-bg);
  border-bottom: 1px solid var(--color-danger-border);
}

.problem-card__header--solution {
  background: var(--color-success-bg);
  border-bottom: 1px solid var(--color-success-border);
}

.problem-card__icon {
  font-size: 1.25rem;
}

.problem-card__title {
  margin: 0;
  font-size: 1.125rem;
  font-weight: 600;
  color: var(--color-heading);
}

.problem-card__body {
  padding: 1.25rem;
}

.problem-card__description {
  font-size: 0.9375rem;
  color: var(--color-text-secondary);
  line-height: 1.6;
  margin-bottom: 1rem;
}

.problem-card__solution-list {
  display: flex;
  flex-direction: column;
  gap: 1rem;
  margin-bottom: 1.25rem;
}

.solution-item {
  padding: 0.75rem 1rem;
  background: var(--color-success-bg);
  border: 1px solid var(--color-success-border);
  border-radius: var(--radius-sm);
}

.solution-item h5 {
  margin: 0 0 0.25rem 0;
  font-size: 0.875rem;
  font-weight: 600;
  color: var(--color-success);
}

.solution-item p {
  margin: 0;
  font-size: 0.8125rem;
  color: var(--color-text-secondary);
  line-height: 1.5;
}

/* ============================================================
   Expandable Sections (Real-World Problems)
   ============================================================ */
.expandable-section {
  margin-top: 1rem;
}

.expandable-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  width: 100%;
  padding: 0.75rem 1rem;
  background: var(--color-bg-secondary);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-sm);
  color: var(--color-text);
  font-size: 0.875rem;
  font-weight: 600;
  cursor: pointer;
  transition: all var(--transition-fast);
}

.expandable-header:hover {
  background: var(--color-bg-tertiary);
}

.expandable-icon {
  font-size: 0.75rem;
  transition: transform var(--transition-fast);
}

.expandable-content {
  display: none;
  padding-top: 1rem;
}

.expandable-section .expandable-content {
  display: block;
}

@media (max-width: 768px) {
  .expandable-content {
    max-height: none !important;
    overflow: visible !important;
  }
}

/* ============================================================
   SCENARIO STEPS (Interview Simulator)
   ============================================================ */
.scenario-steps {
  margin-top: 1.5rem;
}

.scenario-step {
  display: none;
  padding: 1rem 1.25rem;
  margin-bottom: .75rem;
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-left: 4px solid var(--color-primary);
  border-radius: var(--radius-md);
  animation: fadeInUp 0.3s ease;
}

.scenario-step.is-visible {
  display: block;
}

.scenario-step__number {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 28px;
  height: 28px;
  background: var(--color-primary);
  color: #fff;
  border-radius: 50%;
  font-size: .8125rem;
  font-weight: 600;
  margin-right: .75rem;
  flex-shrink: 0;
}

.scenario-step__text {
  font-size: .9375rem;
  color: var(--color-text);
  line-height: 1.6;
}

.scenario-next-btn {
  display: inline-flex !important;
  visibility: visible !important;
  opacity: 1 !important;
  align-items: center;
  gap: .5rem;
  padding: .75rem 1.5rem;
  background: var(--color-primary);
  color: #fff;
  border: none;
  border-radius: var(--radius-md);
  font-size: .9375rem;
  font-weight: 500;
  cursor: pointer;
  transition: all var(--transition-fast);
  margin-top: 1rem;
  text-decoration: none;
}

.scenario-next-btn:hover {
  background: var(--color-primary-hover);
  transform: translateY(-1px);
}

.scenario-next-btn:disabled {
  opacity: .5;
  cursor: not-allowed;
  transform: none;
}

@keyframes fadeInUp {
  from {
    opacity: 0;
    transform: translateY(10px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}