/* ============================================================
   common.css — LLM 3D Academy Shared CSS Foundation
   ============================================================
   Import this file in every page to get the full design system:
     <link rel="stylesheet" href="css/common.css">
   ============================================================ */

/* ----------------------------------------------------------
   1. CSS Custom Properties (Design Tokens)
   ---------------------------------------------------------- */
:root {
  /* ---- Color Palette ---- */

  /* Backgrounds */
  --bg-primary: #08080e;
  --bg-secondary: #0f0f1a;
  --bg-tertiary: #161625;
  --bg-elevated: #1c1c30;

  /* Component accent colors */
  --color-embed: #e8706e;
  --color-pos-enc: #f4a261;
  --color-attention: #ffd166;
  --color-add-norm: #b5e48c;
  --color-ffn: #90caf9;
  --color-linear: #b39ddb;
  --color-softmax: #4dd0e1;

  /* Text — four-level opacity scale */
  --text-primary: rgba(255, 255, 255, 0.9);
  --text-secondary: rgba(255, 255, 255, 0.6);
  --text-tertiary: rgba(255, 255, 255, 0.45);
  --text-muted: rgba(255, 255, 255, 0.35);

  /* Semantic colors */
  --color-success: #b5e48c;
  --color-warning: #f4a261;
  --color-error: #e8706e;
  --color-info: #90caf9;

  /* Border */
  --border-color: rgba(255, 255, 255, 0.08);
  --border-color-hover: rgba(255, 255, 255, 0.16);

  /* ---- Typography ---- */
  --font-sans: -apple-system, BlinkMacSystemFont, 'SF Pro Text', 'Segoe UI', system-ui, sans-serif;
  --font-mono: 'SF Mono', ui-monospace, 'JetBrains Mono', monospace;

  --text-xs: 0.75rem;    /* 12px */
  --text-sm: 0.875rem;   /* 14px */
  --text-base: 1rem;     /* 16px */
  --text-lg: 1.125rem;   /* 18px */
  --text-xl: 1.25rem;    /* 20px */
  --text-2xl: 1.5rem;    /* 24px */
  --text-3xl: 2rem;      /* 32px */

  --leading-tight: 1.25;
  --leading-normal: 1.5;
  --leading-relaxed: 1.75;

  /* ---- Spacing Scale ---- */
  --space-1: 0.25rem;   /* 4px */
  --space-2: 0.5rem;    /* 8px */
  --space-3: 0.75rem;   /* 12px */
  --space-4: 1rem;      /* 16px */
  --space-5: 1.25rem;   /* 20px */
  --space-6: 1.5rem;    /* 24px */
  --space-8: 2rem;      /* 32px */
  --space-10: 2.5rem;   /* 40px */
  --space-12: 3rem;     /* 48px */
  --space-16: 4rem;     /* 64px */

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

  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.4);
  --shadow-md: 0 4px 12px rgba(0, 0, 0, 0.5);
  --shadow-lg: 0 8px 24px rgba(0, 0, 0, 0.6);
  --shadow-glow: 0 0 20px rgba(144, 202, 249, 0.15);

  /* ---- Animation ---- */
  --duration-instant: 100ms;
  --duration-fast: 200ms;
  --duration-normal: 300ms;
  --duration-slow: 500ms;
  --duration-slower: 800ms;

  --ease-default: cubic-bezier(0.4, 0, 0.2, 1);
  --ease-in: cubic-bezier(0.4, 0, 1, 1);
  --ease-out: cubic-bezier(0, 0, 0.2, 1);
  --ease-bounce: cubic-bezier(0.34, 1.56, 0.64, 1);

  /* ---- Z-Index Scale ---- */
  --z-base: 0;
  --z-dropdown: 100;
  --z-sticky: 200;
  --z-overlay: 300;
  --z-modal: 400;
  --z-tooltip: 500;

  /* ---- Container ---- */
  --container-max: 1200px;
  --container-narrow: 800px;
}

/* ----------------------------------------------------------
   2. CSS Reset
   ---------------------------------------------------------- */
*,
*::before,
*::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

html {
  font-size: 16px;
  -webkit-text-size-adjust: 100%;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  text-rendering: optimizeLegibility;
  scroll-behavior: smooth;
}

body {
  font-family: var(--font-sans);
  font-size: var(--text-base);
  line-height: var(--leading-normal);
  color: var(--text-primary);
  background-color: var(--bg-primary);
  min-height: 100vh;
  overflow-x: hidden;
}

a {
  color: var(--color-info);
  text-decoration: none;
  transition: color var(--duration-fast) var(--ease-default);
}

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

img,
svg {
  display: block;
  max-width: 100%;
}

button,
input,
select,
textarea {
  font: inherit;
  color: inherit;
}

ul,
ol {
  list-style: none;
}

h1, h2, h3, h4, h5, h6 {
  font-weight: 600;
  line-height: var(--leading-tight);
  color: var(--text-primary);
}

h1 { font-size: var(--text-3xl); }
h2 { font-size: var(--text-2xl); }
h3 { font-size: var(--text-xl); }
h4 { font-size: var(--text-lg); }

code,
pre,
kbd {
  font-family: var(--font-mono);
}

/* ----------------------------------------------------------
   3. Scrollbar Styles
   ---------------------------------------------------------- */
::-webkit-scrollbar {
  width: 6px;
  height: 6px;
}

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

::-webkit-scrollbar-thumb {
  background: rgba(255, 255, 255, 0.15);
  border-radius: var(--radius-full);
}

::-webkit-scrollbar-thumb:hover {
  background: rgba(255, 255, 255, 0.25);
}

/* Firefox */
* {
  scrollbar-width: thin;
  scrollbar-color: rgba(255, 255, 255, 0.15) var(--bg-secondary);
}

/* ----------------------------------------------------------
   4. Panel Container
   ---------------------------------------------------------- */
.panel {
  background: var(--bg-secondary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-lg);
  padding: var(--space-6);
  transition: border-color var(--duration-fast) var(--ease-default),
              box-shadow var(--duration-fast) var(--ease-default);
}

.panel:hover {
  border-color: var(--border-color-hover);
}

.panel--elevated {
  background: var(--bg-elevated);
  box-shadow: var(--shadow-md);
}

.panel--compact {
  padding: var(--space-4);
}

.panel-header {
  display: flex;
  align-items: center;
  gap: var(--space-3);
  margin-bottom: var(--space-4);
  padding-bottom: var(--space-3);
  border-bottom: 1px solid var(--border-color);
}

.panel-title {
  font-size: var(--text-lg);
  font-weight: 600;
  color: var(--text-primary);
}

.panel-body {
  font-size: var(--text-sm);
  color: var(--text-secondary);
  line-height: var(--leading-relaxed);
}

/* ----------------------------------------------------------
   5. Buttons
   ---------------------------------------------------------- */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-2);
  padding: var(--space-2) var(--space-4);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  background: var(--bg-tertiary);
  color: var(--text-primary);
  font-size: var(--text-sm);
  font-weight: 500;
  cursor: pointer;
  transition: all var(--duration-fast) var(--ease-default);
  user-select: none;
  white-space: nowrap;
}

.btn:hover {
  background: var(--bg-elevated);
  border-color: var(--border-color-hover);
  box-shadow: var(--shadow-sm);
}

.btn:active {
  transform: scale(0.97);
}

.btn--primary {
  background: var(--color-info);
  color: var(--bg-primary);
  border-color: var(--color-info);
}

.btn--primary:hover {
  background: var(--color-ffn);
  border-color: var(--color-ffn);
}

.btn--sm {
  padding: var(--space-1) var(--space-2);
  font-size: var(--text-xs);
  border-radius: var(--radius-sm);
}

.btn--lg {
  padding: var(--space-3) var(--space-6);
  font-size: var(--text-base);
}

.btn--ghost {
  background: transparent;
  border-color: transparent;
}

.btn--ghost:hover {
  background: rgba(255, 255, 255, 0.06);
  border-color: transparent;
}

/* ----------------------------------------------------------
   6. Tags / Labels
   ---------------------------------------------------------- */
.tag {
  display: inline-flex;
  align-items: center;
  gap: var(--space-1);
  padding: 2px var(--space-2);
  border-radius: var(--radius-sm);
  font-size: var(--text-xs);
  font-weight: 500;
  font-family: var(--font-mono);
  white-space: nowrap;
}

.tag--embed     { background: rgba(232, 112, 110, 0.15); color: var(--color-embed); }
.tag--pos-enc   { background: rgba(244, 162, 97, 0.15);  color: var(--color-pos-enc); }
.tag--attention { background: rgba(255, 209, 102, 0.15);  color: var(--color-attention); }
.tag--add-norm  { background: rgba(181, 228, 140, 0.15); color: var(--color-add-norm); }
.tag--ffn       { background: rgba(144, 202, 249, 0.15); color: var(--color-ffn); }
.tag--linear    { background: rgba(179, 157, 219, 0.15); color: var(--color-linear); }
.tag--softmax   { background: rgba(77, 208, 225, 0.15); color: var(--color-softmax); }

/* ----------------------------------------------------------
   7. Formula Block
   ---------------------------------------------------------- */
.formula {
  background: var(--bg-tertiary);
  border: 1px solid var(--border-color);
  border-left: 3px solid var(--color-info);
  border-radius: var(--radius-md);
  padding: var(--space-4) var(--space-5);
  margin: var(--space-4) 0;
  font-family: var(--font-mono);
  font-size: var(--text-sm);
  color: var(--text-primary);
  line-height: var(--leading-relaxed);
  overflow-x: auto;
}

.formula__label {
  display: block;
  margin-bottom: var(--space-2);
  font-size: var(--text-xs);
  font-family: var(--font-sans);
  color: var(--text-tertiary);
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

/* ----------------------------------------------------------
   8. Data Table
   ---------------------------------------------------------- */
.data-table {
  width: 100%;
  border-collapse: collapse;
  font-size: var(--text-sm);
}

.data-table thead th {
  padding: var(--space-3) var(--space-4);
  text-align: left;
  font-size: var(--text-xs);
  font-weight: 600;
  color: var(--text-secondary);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  border-bottom: 1px solid var(--border-color);
  background: var(--bg-tertiary);
}

.data-table tbody td {
  padding: var(--space-3) var(--space-4);
  border-bottom: 1px solid var(--border-color);
  color: var(--text-secondary);
  transition: background var(--duration-instant) var(--ease-default);
}

.data-table tbody tr:hover td {
  background: rgba(255, 255, 255, 0.03);
  color: var(--text-primary);
}

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

/* Numeric cells — right-aligned, monospace */
.data-table .num {
  font-family: var(--font-mono);
  text-align: right;
}

/* ----------------------------------------------------------
   9. Step Labels
   ---------------------------------------------------------- */
.step {
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
  font-size: var(--text-sm);
  color: var(--text-secondary);
}

.step__number {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 24px;
  height: 24px;
  border-radius: var(--radius-full);
  background: var(--bg-tertiary);
  border: 1px solid var(--border-color);
  font-size: var(--text-xs);
  font-weight: 600;
  color: var(--text-primary);
}

.step--active .step__number {
  background: var(--color-info);
  border-color: var(--color-info);
  color: var(--bg-primary);
}

.step--complete .step__number {
  background: var(--color-success);
  border-color: var(--color-success);
  color: var(--bg-primary);
}

/* ----------------------------------------------------------
   10. Animation Keyframes
   ---------------------------------------------------------- */
@keyframes fadeIn {
  from {
    opacity: 0;
  }
  to {
    opacity: 1;
  }
}

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

@keyframes glow {
  0%,
  100% {
    box-shadow: 0 0 8px rgba(144, 202, 249, 0.2);
  }
  50% {
    box-shadow: 0 0 20px rgba(144, 202, 249, 0.4);
  }
}

/* Animation utility classes */
.animate-fade-in {
  animation: fadeIn var(--duration-normal) var(--ease-out) both;
}

.animate-slide-up {
  animation: slideUp var(--duration-normal) var(--ease-out) both;
}

.animate-glow {
  animation: glow 2s var(--ease-default) infinite;
}

/* Staggered children */
.stagger > *:nth-child(1)  { animation-delay: 0ms; }
.stagger > *:nth-child(2)  { animation-delay: 60ms; }
.stagger > *:nth-child(3)  { animation-delay: 120ms; }
.stagger > *:nth-child(4)  { animation-delay: 180ms; }
.stagger > *:nth-child(5)  { animation-delay: 240ms; }
.stagger > *:nth-child(6)  { animation-delay: 300ms; }
.stagger > *:nth-child(7)  { animation-delay: 360ms; }
.stagger > *:nth-child(8)  { animation-delay: 420ms; }
.stagger > *:nth-child(9)  { animation-delay: 480ms; }
.stagger > *:nth-child(10) { animation-delay: 540ms; }

/* ----------------------------------------------------------
   11. Utility Classes
   ---------------------------------------------------------- */
.container {
  width: 100%;
  max-width: var(--container-max);
  margin-inline: auto;
  padding-inline: var(--space-4);
}

.container--narrow {
  max-width: var(--container-narrow);
}

.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border-width: 0;
}

.truncate {
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}

/* ----------------------------------------------------------
   12. Responsive Breakpoints
   ---------------------------------------------------------- */

/* Tablet: ≤ 768px */
@media (max-width: 768px) {
  :root {
    --space-4: 0.875rem;
    --space-6: 1.25rem;
    --space-8: 1.75rem;
  }

  .panel {
    padding: var(--space-4);
    border-radius: var(--radius-md);
  }

  h1 { font-size: 1.75rem; }
  h2 { font-size: 1.375rem; }

  .data-table {
    font-size: var(--text-xs);
  }

  .data-table thead th,
  .data-table tbody td {
    padding: var(--space-2) var(--space-3);
  }
}

/* Mobile: ≤ 480px */
@media (max-width: 480px) {
  :root {
    --space-4: 0.75rem;
    --space-6: 1rem;
  }

  .panel {
    padding: var(--space-3);
    border-radius: var(--radius-sm);
  }

  .panel-header {
    flex-direction: column;
    align-items: flex-start;
  }

  h1 { font-size: 1.5rem; }
  h2 { font-size: 1.25rem; }
  h3 { font-size: 1.125rem; }

  .btn {
    padding: var(--space-2) var(--space-3);
    font-size: var(--text-xs);
  }

  .formula {
    padding: var(--space-3);
    font-size: var(--text-xs);
  }

  .container {
    padding-inline: var(--space-3);
  }

  /* Force table to scroll horizontally */
  .data-table-wrapper {
    overflow-x: auto;
    -webkit-overflow-scrolling: touch;
  }
}

/* ----------------------------------------------------------
   13. Responsive Navigation Bar
   ---------------------------------------------------------- */

/* --- Custom properties for navbar --- */
:root {
  --nav-height: 56px;
  --nav-bg: rgba(10, 10, 18, 0.92);
  --nav-border: rgba(255, 255, 255, 0.06);
  --nav-link-hover: rgba(255, 255, 255, 0.08);
  --nav-link-active-bg: rgba(144, 202, 249, 0.12);
  --nav-link-active-color: var(--color-info);
  --nav-sidebar-width: 280px;
}

/* --- Main nav container --- */
.nav {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  height: var(--nav-height);
  background: var(--nav-bg);
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
  border-bottom: 1px solid var(--nav-border);
  z-index: var(--z-sticky);
  user-select: none;
}

.nav__inner {
  display: flex;
  align-items: center;
  height: 100%;
  max-width: var(--container-max);
  margin: 0 auto;
  padding: 0 var(--space-4);
  gap: var(--space-3);
}

/* --- Logo --- */
.nav__logo {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  text-decoration: none;
  color: var(--text-primary);
  font-weight: 700;
  font-size: var(--text-lg);
  white-space: nowrap;
  flex-shrink: 0;
  transition: opacity var(--duration-fast) var(--ease-default);
}

.nav__logo:hover {
  opacity: 0.8;
  color: var(--text-primary);
}

.nav__logo-icon {
  font-size: 22px;
  line-height: 1;
}

.nav__logo-text {
  letter-spacing: -0.02em;
}

/* --- Desktop nav group buttons --- */
.nav__groups {
  display: flex;
  align-items: center;
  gap: var(--space-1);
  justify-content: center;
  flex: 1;
  list-style: none;
  margin: 0;
  padding: 0;
}

.nav__group {
  position: relative;
  flex-shrink: 0;
}

.nav__group-btn {
  display: flex;
  align-items: center;
  gap: 5px;
  padding: var(--space-1) var(--space-3);
  border-radius: var(--radius-md);
  font-size: var(--text-sm);
  font-weight: 500;
  color: var(--text-secondary);
  background: transparent;
  border: none;
  cursor: pointer;
  white-space: nowrap;
  transition: background var(--duration-fast) var(--ease-default),
              color var(--duration-fast) var(--ease-default);
}

.nav__group-btn:hover {
  background: var(--nav-link-hover);
  color: var(--text-primary);
}

.nav__group--active > .nav__group-btn {
  background: var(--nav-link-active-bg);
  color: var(--nav-link-active-color);
}

.nav__group--active > .nav__group-btn:hover {
  background: var(--nav-link-active-bg);
  color: var(--nav-link-active-color);
}

.nav__group-btn:focus-visible {
  box-shadow: 0 0 0 2px rgba(144, 202, 249, 0.5);
  outline: none;
}

/* --- Dropdown panel --- */
.nav__dropdown {
  position: absolute;
  top: 100%;
  left: 0;
  min-width: 200px;
  background: rgba(10, 10, 18, 0.98);
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
  border: 1px solid rgba(255, 255, 255, 0.1);
  border-radius: 0 0 var(--radius-md) var(--radius-md);
  padding: var(--space-1) 0;
  opacity: 0;
  visibility: hidden;
  transform: translateY(-4px);
  transition: opacity var(--duration-fast) var(--ease-default),
              visibility var(--duration-fast) var(--ease-default),
              transform var(--duration-fast) var(--ease-default);
  z-index: var(--z-dropdown);
}

.nav__dropdown-list {
  list-style: none;
  margin: 0;
  padding: 0;
}

.nav__group:hover > .nav__dropdown,
.nav__group:focus-within > .nav__dropdown,
.nav__group--open > .nav__dropdown {
  opacity: 1;
  visibility: visible;
  transform: translateY(0);
}

.nav__dropdown .nav__item {
  /* no special shrink needed */
}

.nav__dropdown .nav__link {
  padding: var(--space-2) var(--space-4);
  border-radius: 0;
}

/* --- Shared nav link styles --- */
.nav__item {
  flex-shrink: 0;
}

.nav__link {
  display: flex;
  align-items: center;
  gap: 5px;
  padding: var(--space-1) var(--space-3);
  border-radius: var(--radius-md);
  font-size: var(--text-sm);
  font-weight: 500;
  color: var(--text-secondary);
  text-decoration: none;
  white-space: nowrap;
  transition: background var(--duration-fast) var(--ease-default),
              color var(--duration-fast) var(--ease-default);
}

.nav__link:hover {
  background: var(--nav-link-hover);
  color: var(--text-primary);
  text-decoration: none;
}

.nav__link--active {
  background: var(--nav-link-active-bg);
  color: var(--nav-link-active-color);
}

.nav__link--active:hover {
  background: var(--nav-link-active-bg);
  color: var(--nav-link-active-color);
}

.nav__icon {
  font-size: 16px;
  line-height: 1;
  flex-shrink: 0;
}

.nav__label {
  line-height: 1;
}

/* --- Right actions (lang + hamburger) --- */
.nav__actions {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  flex-shrink: 0;
  margin-left: auto;
}

/* --- Language button --- */
.nav__lang-btn {
  display: flex;
  align-items: center;
  gap: 4px;
  padding: var(--space-1) var(--space-2);
  background: rgba(255, 255, 255, 0.05);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  color: var(--text-secondary);
  font-size: var(--text-xs);
  font-weight: 600;
  cursor: pointer;
  transition: all var(--duration-fast) var(--ease-default);
  white-space: nowrap;
}

.nav__lang-btn:hover {
  background: rgba(255, 255, 255, 0.1);
  color: var(--text-primary);
  border-color: var(--border-color-hover);
}

.nav__lang-btn:focus-visible {
  box-shadow: 0 0 0 2px rgba(144, 202, 249, 0.5);
  outline: none;
}

.nav__lang-icon {
  font-size: 14px;
  line-height: 1;
}

.nav__lang-label {
  min-width: 18px;
  text-align: center;
}

/* --- Hamburger button (hidden on desktop) --- */
.nav__hamburger {
  display: none;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  gap: 5px;
  width: 40px;
  height: 40px;
  background: transparent;
  border: none;
  cursor: pointer;
  padding: 8px;
  border-radius: var(--radius-md);
  transition: background var(--duration-fast) var(--ease-default);
}

.nav__hamburger:hover {
  background: var(--nav-link-hover);
}

.nav__hamburger:focus-visible {
  box-shadow: 0 0 0 2px rgba(144, 202, 249, 0.5);
  outline: none;
}

.nav__hamburger-line {
  display: block;
  width: 20px;
  height: 2px;
  background: var(--text-secondary);
  border-radius: 1px;
  transition: all var(--duration-normal) var(--ease-default);
}

/* Hamburger active state (X shape) */
.nav__hamburger--active .nav__hamburger-line:nth-child(1) {
  transform: translateY(7px) rotate(45deg);
}

.nav__hamburger--active .nav__hamburger-line:nth-child(2) {
  opacity: 0;
}

.nav__hamburger--active .nav__hamburger-line:nth-child(3) {
  transform: translateY(-7px) rotate(-45deg);
}

/* --- Mobile sidebar overlay --- */
.nav-overlay {
  position: fixed;
  inset: 0;
  background: rgba(0, 0, 0, 0.6);
  z-index: calc(var(--z-sticky) + 1);
  opacity: 0;
  visibility: hidden;
  transition: opacity var(--duration-normal) var(--ease-default),
              visibility var(--duration-normal) var(--ease-default);
}

.nav-overlay--visible {
  opacity: 1;
  visibility: visible;
}

/* --- Mobile sidebar --- */
.nav-sidebar {
  position: fixed;
  top: 0;
  left: 0;
  bottom: 0;
  width: var(--nav-sidebar-width);
  max-width: 85vw;
  background: rgba(10, 10, 18, 0.97);
  backdrop-filter: blur(24px);
  -webkit-backdrop-filter: blur(24px);
  border-right: 1px solid var(--nav-border);
  z-index: calc(var(--z-sticky) + 2);
  transform: translateX(-100%);
  transition: transform var(--duration-normal) var(--ease-default);
  display: flex;
  flex-direction: column;
  overflow-y: auto;
}

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

.nav-sidebar__header {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  padding: var(--space-4) var(--space-4) var(--space-3);
  border-bottom: 1px solid var(--nav-border);
  font-weight: 700;
  font-size: var(--text-lg);
  color: var(--text-primary);
}

.nav-sidebar__close {
  margin-left: auto;
  width: 32px;
  height: 32px;
  display: flex;
  align-items: center;
  justify-content: center;
  background: rgba(255, 255, 255, 0.05);
  border: none;
  border-radius: var(--radius-md);
  color: var(--text-secondary);
  font-size: var(--text-lg);
  cursor: pointer;
  transition: all var(--duration-fast) var(--ease-default);
}

.nav-sidebar__close:hover {
  background: rgba(255, 255, 255, 0.12);
  color: var(--text-primary);
}

.nav-sidebar__links {
  list-style: none;
  margin: 0;
  padding: var(--space-2) 0;
  flex: 1;
}

.nav-sidebar__links .nav__item {
  /* override flex-shrink for sidebar */
}

.nav-sidebar__links > .nav__item > .nav__link {
  padding: var(--space-3) var(--space-4);
  border-radius: 0;
  font-size: var(--text-base);
}

.nav-sidebar__links > .nav__item > .nav__link .nav__icon {
  font-size: 18px;
}

.nav-sidebar__links .nav__link--active {
  background: var(--nav-link-active-bg);
  border-left: 3px solid var(--nav-link-active-color);
}

/* --- Mobile sidebar grouped sections --- */
.nav-sidebar__group-item {
  margin: 0;
}

.nav-sidebar__group {
  margin: 0;
}

.nav-sidebar__group summary {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  padding: var(--space-3) var(--space-4);
  font-size: var(--text-sm);
  font-weight: 600;
  color: var(--text-secondary);
  cursor: pointer;
  list-style: none;
  user-select: none;
  transition: background var(--duration-fast) var(--ease-default),
              color var(--duration-fast) var(--ease-default);
}

.nav-sidebar__group summary::-webkit-details-marker {
  display: none;
}

.nav-sidebar__group summary:hover {
  background: var(--nav-link-hover);
  color: var(--text-primary);
}

.nav-sidebar__group summary .nav__icon {
  font-size: 18px;
}

.nav-sidebar__group-chevron {
  margin-left: auto;
  font-size: 12px;
  color: var(--text-tertiary);
  transition: transform var(--duration-normal) var(--ease-default);
}

.nav-sidebar__group[open] summary .nav-sidebar__group-chevron {
  transform: rotate(180deg);
}

.nav-sidebar__group-links {
  list-style: none;
  margin: 0;
  padding: 0;
}

.nav-sidebar__group-links .nav__link {
  padding: var(--space-2) var(--space-4) var(--space-2) var(--space-8);
  font-size: var(--text-sm);
}

.nav-sidebar__group-links .nav__icon {
  font-size: 16px;
}

.nav-sidebar__footer {
  padding: var(--space-3) var(--space-4);
  border-top: 1px solid var(--nav-border);
}

.nav__lang-btn--sidebar {
  width: 100%;
  justify-content: center;
  padding: var(--space-2) var(--space-4);
  font-size: var(--text-sm);
}

/* --- Responsive: Tablet (≤ 900px) --- */
@media (max-width: 900px) {
  .nav__group-btn {
    padding: var(--space-1) var(--space-2);
    font-size: var(--text-xs);
    gap: 3px;
  }

  .nav__logo-text {
    font-size: var(--text-base);
  }
}

/* --- Responsive: Mobile (≤ 768px) — switch to hamburger --- */
@media (max-width: 768px) {
  :root {
    --nav-height: 52px;
  }

  .nav__groups {
    display: none;
  }

  .nav__hamburger {
    display: flex;
  }

  .nav__logo-text {
    font-size: var(--text-base);
  }
}

/* --- Responsive: Small mobile (≤ 480px) --- */
@media (max-width: 480px) {
  .nav__inner {
    padding: 0 var(--space-3);
  }

  .nav__logo {
    font-size: var(--text-base);
    gap: var(--space-1);
  }

  .nav__logo-icon {
    font-size: 18px;
  }
}

/* ----------------------------------------------------------
   14. Mobile Touch Targets & Interaction
   ---------------------------------------------------------- */

/* Ensure all interactive elements meet 44×44px minimum touch target */
@media (max-width: 768px) {
  .btn {
    min-height: 44px;
    min-width: 44px;
  }

  .btn--sm {
    min-height: 36px;
    padding: var(--space-2) var(--space-3);
  }

  .tag {
    padding: 4px var(--space-2);
    min-height: 24px;
  }

  /* Step number circles — ensure tap-friendly */
  .step__number {
    width: 28px;
    height: 28px;
    font-size: var(--text-xs);
  }

  .step {
    font-size: var(--text-sm);
    min-height: 28px;
  }
}

/* ----------------------------------------------------------
   16. Sub-page Mobile Layout Overrides
   ---------------------------------------------------------- */

@media (max-width: 768px) {
  /* === Back button === */
  #backBtn {
    top: calc(var(--nav-height, 56px) + 10px) !important;
    left: 16px !important;
    padding: 8px 14px !important;
    font-size: 12px !important;
    min-height: 40px !important;
  }
}

/* ----------------------------------------------------------
   20. Course Card Touch Target (Homepage)
   ---------------------------------------------------------- */
@media (max-width: 768px) {
  .course-card {
    min-height: 44px;
    /* Make entire card a good touch target since it's an <a> tag */
  }

  .course-card__cta-arrow,
  .course-card__footer {
    min-height: 28px;
  }
}

/* ----------------------------------------------------------
    22. Module Prev/Next Navigation
    ---------------------------------------------------------- */
.module-nav {
  position: fixed;
  bottom: 0;
  left: 0;
  right: 0;
  z-index: var(--z-sticky);
  background: rgba(10, 10, 18, 0.92);
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
  border-top: 1px solid rgba(255, 255, 255, 0.06);
  padding: var(--space-3) var(--space-4);
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--space-4);
}

.module-nav__link {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  padding: var(--space-2) var(--space-3);
  border-radius: var(--radius-md);
  color: var(--text-secondary);
  text-decoration: none;
  font-size: var(--text-sm);
  font-weight: 500;
  transition: all var(--duration-fast) var(--ease-default);
  white-space: nowrap;
  max-width: 40%;
  overflow: hidden;
  text-overflow: ellipsis;
}

.module-nav__link:hover {
  color: var(--color-info);
  background: rgba(144, 202, 249, 0.08);
  text-decoration: none;
}

.module-nav__link--prev {
  justify-content: flex-start;
}

.module-nav__link--next {
  justify-content: flex-end;
  text-align: right;
  margin-left: auto;
}

.module-nav__arrow {
  font-size: var(--text-lg);
  line-height: 1;
  flex-shrink: 0;
}

.module-nav__info {
  flex-shrink: 0;
  text-align: center;
}

.module-nav__counter {
  font-size: var(--text-xs);
  color: var(--text-tertiary);
  font-family: var(--font-mono);
}

.module-nav__name {
  display: block;
  max-width: 140px;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}

@media (max-width: 768px) {
  .module-nav {
    padding: var(--space-2) var(--space-3);
    bottom: 0;
  }

  .module-nav__link {
    font-size: var(--text-xs);
    padding: var(--space-1) var(--space-2);
  }

  .module-nav__name {
    max-width: 80px;
  }

  .module-nav__counter {
    font-size: 10px;
  }
}

@media (max-width: 480px) {
  .module-nav__name {
    max-width: 60px;
  }
}



/* ----------------------------------------------------------
    25. Module Page Base Styles
    ---------------------------------------------------------- */

/* Module page base */
html, body { overflow: hidden; height: 100%; }
body { background: #111827; font-family: -apple-system, BlinkMacSystemFont, 'SF Pro Text', 'Segoe UI', system-ui, sans-serif; color: #e0e0ec; user-select: none; padding-top: var(--nav-height, 56px) !important; }

/* ===========================================================
   Reduced Motion — Accessibility (prefers-reduced-motion)
   =========================================================== */
@media (prefers-reduced-motion: reduce) {
  /* Disable all @keyframes animations */
  *, *::before, *::after {
    animation-duration: 0.001ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.001ms !important;
    scroll-behavior: auto !important;
  }

  /* Keep layout transforms, just skip the animated entrance */
  .stagger > * { animation-delay: 0ms !important; }
}