/* ==========================================================================
   College Online — Platform CSS
   Dark theme, responsive, no dependencies
   ========================================================================== */

/* --- Reset & Variables --- */
:root {
  --bg: #0f0f13;
  --bg-elevated: #13131a;
  --surface: #1a1a24;
  --surface2: #22223a;
  --surface3: #2a2a42;
  --border: #2e2e4a;
  --border-light: #3a3a58;
  --text: #e4e4ef;
  --text-muted: #8888a8;
  --text-dim: #5e5e78;
  --accent: #6c63ff;
  --accent-light: #8b83ff;
  --accent-glow: rgba(108, 99, 255, 0.15);
  --accent-glow-strong: rgba(108, 99, 255, 0.25);
  --green: #34d399;
  --green-dim: rgba(52, 211, 153, 0.15);
  --yellow: #fbbf24;
  --yellow-dim: rgba(251, 191, 36, 0.15);
  --red: #f87171;
  --blue: #60a5fa;
  --orange: #fb923c;
  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 14px;
  --radius-xl: 20px;
  --shadow-sm: 0 1px 3px rgba(0,0,0,0.3);
  --shadow-md: 0 4px 12px rgba(0,0,0,0.4);
  --shadow-lg: 0 8px 30px rgba(0,0,0,0.5);
  --transition: 0.2s ease;
  --font: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
  --font-mono: 'JetBrains Mono', 'Fira Code', 'Cascadia Code', monospace;
  --sidebar-width: 280px;
  --topbar-height: 60px;
}

*, *::before, *::after {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

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

body {
  font-family: var(--font);
  background: var(--bg);
  color: var(--text);
  line-height: 1.65;
  min-height: 100vh;
  overflow-x: hidden;
  -webkit-font-smoothing: antialiased;
}

a {
  color: var(--accent-light);
  text-decoration: none;
  transition: color var(--transition);
}

a:hover { color: #a99fff; }

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

/* --- Typography --- */
h1, h2, h3, h4, h5 {
  font-weight: 600;
  line-height: 1.3;
  color: var(--text);
}

h1 { font-size: 2.2rem; }
h2 { font-size: 1.6rem; }
h3 { font-size: 1.2rem; }
h4 { font-size: 1rem; }

/* --- Top Bar --- */
.topbar {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  height: var(--topbar-height);
  background: rgba(15, 15, 19, 0.92);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--border);
  display: flex;
  align-items: center;
  padding: 0 1.5rem;
  z-index: 1000;
  gap: 1rem;
}

.topbar-brand {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  font-weight: 700;
  font-size: 1.1rem;
  color: var(--text);
  text-decoration: none;
  flex-shrink: 0;
}

.topbar-brand svg {
  width: 28px;
  height: 28px;
  color: var(--accent);
}

.topbar-brand span {
  color: var(--accent-light);
}

.topbar-nav {
  display: flex;
  align-items: center;
  gap: 0.25rem;
  margin-left: 1.5rem;
  overflow-x: auto;
  -webkit-overflow-scrolling: touch;
  scrollbar-width: none;
}

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

.topbar-nav a,
.topbar-nav span {
  font-size: 0.85rem;
  color: var(--text-muted);
  white-space: nowrap;
  padding: 0.3rem 0;
}

.topbar-nav a:hover { color: var(--text); }

.topbar-nav .sep {
  color: var(--text-dim);
  margin: 0 0.3rem;
  user-select: none;
}

.topbar-nav .current {
  color: var(--text);
  font-weight: 500;
}

.topbar-right {
  margin-left: auto;
  display: flex;
  align-items: center;
  gap: 0.75rem;
  flex-shrink: 0;
}

.topbar-progress {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  font-size: 0.8rem;
  color: var(--text-muted);
}

.topbar-progress-bar {
  width: 80px;
  height: 4px;
  background: var(--surface2);
  border-radius: 2px;
  overflow: hidden;
}

.topbar-progress-fill {
  height: 100%;
  background: var(--accent);
  border-radius: 2px;
  transition: width 0.5s ease;
}

.btn-menu {
  display: none;
  background: none;
  border: none;
  color: var(--text-muted);
  cursor: pointer;
  padding: 0.4rem;
  border-radius: var(--radius-sm);
  transition: background var(--transition);
}

.btn-menu:hover { background: var(--surface2); }

.btn-menu svg { width: 22px; height: 22px; }

/* --- Sidebar --- */
.sidebar {
  position: fixed;
  top: var(--topbar-height);
  left: 0;
  bottom: 0;
  width: var(--sidebar-width);
  background: var(--bg-elevated);
  border-right: 1px solid var(--border);
  overflow-y: auto;
  overflow-x: hidden;
  padding: 1rem 0;
  z-index: 900;
  transition: transform 0.3s ease;
  scrollbar-width: thin;
  scrollbar-color: var(--surface3) transparent;
}

.sidebar::-webkit-scrollbar { width: 5px; }
.sidebar::-webkit-scrollbar-track { background: transparent; }
.sidebar::-webkit-scrollbar-thumb { background: var(--surface3); border-radius: 3px; }

.sidebar-section {
  padding: 0 0.75rem;
  margin-bottom: 1.25rem;
}

.sidebar-title {
  font-size: 0.7rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--text-dim);
  padding: 0 0.75rem;
  margin-bottom: 0.5rem;
}

.sidebar-item {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  padding: 0.5rem 0.75rem;
  border-radius: var(--radius-sm);
  color: var(--text-muted);
  font-size: 0.88rem;
  cursor: pointer;
  transition: all var(--transition);
  text-decoration: none;
  position: relative;
}

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

.sidebar-item.active {
  background: var(--accent-glow);
  color: var(--accent-light);
  font-weight: 500;
}

.sidebar-item .status-dot {
  width: 7px;
  height: 7px;
  border-radius: 50%;
  flex-shrink: 0;
}

.sidebar-item .status-dot.done { background: var(--green); }
.sidebar-item .status-dot.in-progress { background: var(--yellow); }
.sidebar-item .status-dot.locked { background: var(--text-dim); }

.sidebar-item .icon {
  width: 18px;
  height: 18px;
  flex-shrink: 0;
  opacity: 0.6;
}

.sidebar-module {
  padding: 0.4rem 0.75rem 0.4rem 1.2rem;
  font-size: 0.82rem;
  font-weight: 500;
  color: var(--text-muted);
  margin-top: 0.25rem;
  cursor: default;
}

.sidebar-lesson {
  padding: 0.35rem 0.75rem 0.35rem 2rem;
  font-size: 0.82rem;
}

.sidebar-lesson .lesson-number {
  font-size: 0.72rem;
  color: var(--text-dim);
  min-width: 1.4rem;
}

.sidebar-overlay {
  display: none;
  position: fixed;
  inset: 0;
  background: rgba(0,0,0,0.5);
  z-index: 899;
}

/* --- Main Content Area --- */
.main {
  margin-left: var(--sidebar-width);
  margin-top: var(--topbar-height);
  min-height: calc(100vh - var(--topbar-height));
}

.main.no-sidebar {
  margin-left: 0;
}

/* --- Page: Homepage --- */
.hero-home {
  background: linear-gradient(160deg, #1a1a3e 0%, #0f0f13 40%, #141428 100%);
  border-bottom: 1px solid var(--border);
  padding: 4rem 2rem 3.5rem;
  text-align: center;
  position: relative;
  overflow: hidden;
}

.hero-home::before {
  content: '';
  position: absolute;
  top: -50%;
  left: -20%;
  width: 140%;
  height: 200%;
  background: radial-gradient(ellipse at 60% 30%, rgba(108, 99, 255, 0.06) 0%, transparent 60%);
  pointer-events: none;
}

.hero-badge {
  display: inline-block;
  background: var(--accent);
  color: white;
  font-size: 0.72rem;
  font-weight: 700;
  padding: 0.3rem 0.9rem;
  border-radius: 999px;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  margin-bottom: 1.25rem;
}

.hero-home h1 {
  font-size: 2.8rem;
  font-weight: 800;
  line-height: 1.15;
  margin-bottom: 0.75rem;
  letter-spacing: -0.02em;
}

.hero-home h1 span { color: var(--accent-light); }

.hero-home .subtitle {
  color: var(--text-muted);
  font-size: 1.1rem;
  max-width: 580px;
  margin: 0 auto 2rem;
  line-height: 1.6;
}

.hero-stats {
  display: flex;
  justify-content: center;
  gap: 2.5rem;
  flex-wrap: wrap;
}

.hero-stat {
  text-align: center;
}

.hero-stat .value {
  font-size: 2rem;
  font-weight: 700;
  color: var(--accent-light);
}

.hero-stat .label {
  font-size: 0.78rem;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

/* --- Section --- */
.section {
  padding: 3rem 2rem;
  max-width: 1200px;
  margin: 0 auto;
}

.section-header {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  margin-bottom: 1.75rem;
}

.section-header h2 { white-space: nowrap; }

.section-header .line {
  flex: 1;
  height: 1px;
  background: var(--border);
}

/* --- Path Card (homepage) --- */
.path-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  overflow: hidden;
  margin-bottom: 2rem;
  transition: border-color var(--transition);
}

.path-card:hover { border-color: var(--accent); }

.path-card-header {
  padding: 1.5rem 1.75rem;
  background: linear-gradient(135deg, var(--surface2) 0%, var(--surface) 100%);
  border-bottom: 1px solid var(--border);
  display: flex;
  align-items: flex-start;
  gap: 1.25rem;
}

.path-icon {
  width: 52px;
  height: 52px;
  background: var(--accent-glow);
  border: 1px solid rgba(108, 99, 255, 0.3);
  border-radius: var(--radius-md);
  display: flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
}

.path-icon svg {
  width: 26px;
  height: 26px;
  color: var(--accent-light);
}

.path-info { flex: 1; }

.path-info h3 {
  font-size: 1.25rem;
  font-weight: 700;
  margin-bottom: 0.25rem;
}

.path-info .meta {
  font-size: 0.85rem;
  color: var(--text-muted);
}

.path-info .meta span { margin-right: 1rem; }

.path-card-body {
  padding: 1.25rem 1.75rem;
}

/* --- Course Card (inside path or standalone) --- */
.course-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(320px, 1fr));
  gap: 1rem;
}

.course-card {
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  padding: 1.25rem;
  display: flex;
  flex-direction: column;
  gap: 0.75rem;
  transition: all var(--transition);
  text-decoration: none;
  color: inherit;
}

.course-card:hover {
  border-color: var(--accent);
  background: var(--surface);
  transform: translateY(-2px);
  box-shadow: var(--shadow-md);
}

.course-card-top {
  display: flex;
  align-items: flex-start;
  gap: 0.75rem;
}

.course-thumb {
  width: 44px;
  height: 44px;
  background: var(--surface2);
  border-radius: var(--radius-sm);
  display: flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
  font-size: 1.2rem;
}

.course-card h4 {
  font-size: 1rem;
  font-weight: 600;
  line-height: 1.35;
}

.course-card .course-desc {
  font-size: 0.85rem;
  color: var(--text-muted);
  line-height: 1.5;
}

.course-card-footer {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-top: auto;
  padding-top: 0.75rem;
  border-top: 1px solid var(--border);
}

.course-meta {
  display: flex;
  gap: 1rem;
  font-size: 0.78rem;
  color: var(--text-muted);
}

.course-meta span {
  display: flex;
  align-items: center;
  gap: 0.3rem;
}

.course-progress-mini {
  width: 60px;
  height: 4px;
  background: var(--surface2);
  border-radius: 2px;
  overflow: hidden;
}

.course-progress-mini .fill {
  height: 100%;
  background: var(--accent);
  border-radius: 2px;
}

/* --- Course Page: Header --- */
.course-header {
  background: linear-gradient(160deg, #1a1a3e 0%, #0f0f13 50%, #181830 100%);
  border-bottom: 1px solid var(--border);
  padding: 2.5rem 2rem;
}

.course-header .inner {
  max-width: 900px;
}

.course-header .breadcrumb {
  font-size: 0.82rem;
  color: var(--text-muted);
  margin-bottom: 1rem;
}

.course-header .breadcrumb a { color: var(--text-muted); }
.course-header .breadcrumb a:hover { color: var(--accent-light); }
.course-header .breadcrumb .sep { margin: 0 0.4rem; }

.course-header h1 {
  font-size: 2rem;
  font-weight: 800;
  margin-bottom: 0.5rem;
}

.course-header .course-subtitle {
  color: var(--text-muted);
  font-size: 1rem;
  margin-bottom: 1.5rem;
  max-width: 700px;
}

.course-tags {
  display: flex;
  gap: 0.5rem;
  flex-wrap: wrap;
}

.tag {
  display: inline-flex;
  align-items: center;
  gap: 0.3rem;
  padding: 0.25rem 0.7rem;
  border-radius: 999px;
  font-size: 0.75rem;
  font-weight: 500;
  background: var(--surface2);
  color: var(--text-muted);
  border: 1px solid var(--border);
}

.tag.accent {
  background: var(--accent-glow);
  color: var(--accent-light);
  border-color: rgba(108, 99, 255, 0.3);
}

/* --- Course Content Area --- */
.course-content {
  padding: 2rem;
  max-width: 900px;
}

/* --- Module Block --- */
.module-block {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  margin-bottom: 1.25rem;
  overflow: hidden;
  transition: border-color var(--transition);
}

.module-block:hover { border-color: var(--border-light); }

.module-header {
  display: flex;
  align-items: center;
  gap: 1rem;
  padding: 1rem 1.25rem;
  background: var(--surface2);
  border-bottom: 1px solid var(--border);
  cursor: pointer;
  user-select: none;
  transition: background var(--transition);
}

.module-header:hover { background: var(--surface3); }

.module-number {
  width: 36px;
  height: 36px;
  background: var(--accent-glow);
  color: var(--accent-light);
  border-radius: var(--radius-sm);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 0.85rem;
  font-weight: 700;
  flex-shrink: 0;
}

.module-info { flex: 1; }

.module-info h3 {
  font-size: 1rem;
  font-weight: 600;
  margin-bottom: 0.1rem;
}

.module-info .module-meta {
  font-size: 0.78rem;
  color: var(--text-muted);
}

.module-progress {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  font-size: 0.78rem;
  color: var(--text-muted);
  flex-shrink: 0;
}

.module-progress-bar {
  width: 50px;
  height: 4px;
  background: var(--bg);
  border-radius: 2px;
  overflow: hidden;
}

.module-progress-fill {
  height: 100%;
  background: var(--green);
  border-radius: 2px;
  transition: width 0.4s ease;
}

.module-chevron {
  color: var(--text-dim);
  transition: transform 0.2s;
  flex-shrink: 0;
}

.module-block.collapsed .module-body { display: none; }
.module-block.collapsed .module-chevron { transform: rotate(-90deg); }

.module-body {
  padding: 0;
}

/* --- Lesson Row --- */
.lesson-row {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  padding: 0.7rem 1.25rem;
  border-bottom: 1px solid rgba(46, 46, 74, 0.5);
  color: inherit;
  text-decoration: none;
  transition: background var(--transition);
}

.lesson-row:last-child { border-bottom: none; }
.lesson-row:hover { background: rgba(108, 99, 255, 0.04); }

.lesson-check {
  width: 22px;
  height: 22px;
  border: 2px solid var(--border-light);
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
  transition: all var(--transition);
}

.lesson-check.done {
  background: var(--green);
  border-color: var(--green);
}

.lesson-check.done::after {
  content: '';
  width: 8px;
  height: 5px;
  border-left: 2px solid #fff;
  border-bottom: 2px solid #fff;
  transform: rotate(-45deg) translateY(-1px);
}

.lesson-icon {
  width: 20px;
  height: 20px;
  color: var(--text-dim);
  flex-shrink: 0;
}

.lesson-title {
  flex: 1;
  font-size: 0.9rem;
  font-weight: 400;
}

.lesson-title .num {
  color: var(--text-dim);
  font-size: 0.78rem;
  margin-right: 0.4rem;
}

.lesson-duration {
  font-size: 0.75rem;
  color: var(--text-dim);
  flex-shrink: 0;
}

.lesson-type-icon {
  width: 16px;
  height: 16px;
  color: var(--text-dim);
  flex-shrink: 0;
}

/* --- Lesson Page --- */
.lesson-content {
  padding: 2.5rem 2rem;
  max-width: 800px;
  margin: 0 auto;
}

.lesson-content h1 {
  font-size: 1.8rem;
  margin-bottom: 0.5rem;
}

.lesson-content .lesson-meta-bar {
  display: flex;
  align-items: center;
  gap: 1rem;
  font-size: 0.82rem;
  color: var(--text-muted);
  margin-bottom: 2rem;
  padding-bottom: 1.25rem;
  border-bottom: 1px solid var(--border);
}

.lesson-content h2 {
  font-size: 1.35rem;
  margin: 2rem 0 0.75rem;
  padding-top: 1rem;
}

.lesson-content h3 {
  font-size: 1.1rem;
  margin: 1.5rem 0 0.5rem;
}

.lesson-content p {
  margin-bottom: 1rem;
  color: var(--text);
  font-size: 0.95rem;
}

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

.lesson-content li {
  margin-bottom: 0.4rem;
  font-size: 0.95rem;
  color: var(--text);
}

.lesson-content strong { font-weight: 600; }

.lesson-content em { font-style: italic; color: var(--text-muted); }

/* --- Code Blocks --- */
.code-block {
  background: #0d0d11;
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  margin: 1rem 0 1.5rem;
  overflow: hidden;
}

.code-block-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0.5rem 1rem;
  background: var(--surface);
  border-bottom: 1px solid var(--border);
  font-size: 0.75rem;
  color: var(--text-muted);
}

.code-block-header .lang {
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

.btn-copy {
  background: none;
  border: 1px solid var(--border);
  color: var(--text-muted);
  padding: 0.2rem 0.5rem;
  border-radius: var(--radius-sm);
  font-size: 0.72rem;
  cursor: pointer;
  transition: all var(--transition);
}

.btn-copy:hover {
  background: var(--surface2);
  color: var(--text);
}

.code-block pre {
  padding: 1rem 1.25rem;
  overflow-x: auto;
  font-family: var(--font-mono);
  font-size: 0.85rem;
  line-height: 1.6;
  color: var(--text);
  scrollbar-width: thin;
  scrollbar-color: var(--surface3) transparent;
}

.code-block pre code { font-family: inherit; }

/* Inline code */
.lesson-content code {
  font-family: var(--font-mono);
  background: var(--surface2);
  padding: 0.15rem 0.4rem;
  border-radius: 4px;
  font-size: 0.85em;
  color: var(--accent-light);
}

.code-block code {
  background: none;
  padding: 0;
  color: inherit;
}

/* Syntax colors (minimal manual highlighting) */
.kw { color: #c792ea; }
.fn { color: #82aaff; }
.str { color: #c3e88d; }
.cmt { color: #546e7a; font-style: italic; }
.num { color: #f78c6c; }
.type { color: #ffcb6b; }
.op { color: #89ddff; }

/* --- Info / Warning / Tip boxes --- */
.callout-box {
  border-radius: var(--radius-md);
  padding: 1rem 1.25rem;
  margin: 1rem 0 1.5rem;
  display: flex;
  gap: 0.75rem;
  align-items: flex-start;
}

.callout-box .callout-icon {
  font-size: 1.1rem;
  flex-shrink: 0;
  margin-top: 0.1rem;
}

.callout-box .callout-body {
  font-size: 0.9rem;
  line-height: 1.55;
}

.callout-box .callout-body strong {
  display: block;
  margin-bottom: 0.2rem;
}

.callout-info {
  background: rgba(96, 165, 250, 0.08);
  border: 1px solid rgba(96, 165, 250, 0.2);
}

.callout-info .callout-icon { color: var(--blue); }

.callout-warning {
  background: rgba(251, 191, 36, 0.08);
  border: 1px solid rgba(251, 191, 36, 0.2);
}

.callout-warning .callout-icon { color: var(--yellow); }

.callout-tip {
  background: rgba(52, 211, 153, 0.08);
  border: 1px solid rgba(52, 211, 153, 0.2);
}

.callout-tip .callout-icon { color: var(--green); }

/* --- Video Placeholder --- */
.video-placeholder {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 3rem 2rem;
  text-align: center;
  margin: 1.5rem 0;
}

.video-placeholder svg {
  width: 48px;
  height: 48px;
  color: var(--text-dim);
  margin-bottom: 0.75rem;
}

.video-placeholder p {
  color: var(--text-muted);
  font-size: 0.9rem;
}

/* --- Quiz / Exercise --- */
.quiz-block {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 1.5rem;
  margin: 2rem 0;
}

.quiz-block h4 {
  font-size: 0.9rem;
  font-weight: 600;
  margin-bottom: 1rem;
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.quiz-question {
  font-size: 0.95rem;
  margin-bottom: 1rem;
  line-height: 1.55;
}

.quiz-options {
  list-style: none;
  padding: 0;
}

.quiz-option {
  display: flex;
  align-items: flex-start;
  gap: 0.75rem;
  padding: 0.65rem 0.85rem;
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  margin-bottom: 0.5rem;
  cursor: pointer;
  transition: all var(--transition);
  font-size: 0.9rem;
}

.quiz-option:hover {
  background: var(--surface2);
  border-color: var(--border-light);
}

.quiz-option.selected {
  border-color: var(--accent);
  background: var(--accent-glow);
}

.quiz-option.correct {
  border-color: var(--green);
  background: var(--green-dim);
}

.quiz-option.incorrect {
  border-color: var(--red);
  background: rgba(248, 113, 113, 0.1);
}

.quiz-radio {
  width: 18px;
  height: 18px;
  border: 2px solid var(--border-light);
  border-radius: 50%;
  flex-shrink: 0;
  margin-top: 0.1rem;
  transition: all var(--transition);
}

.quiz-option.selected .quiz-radio {
  border-color: var(--accent);
  background: var(--accent);
  box-shadow: inset 0 0 0 3px var(--surface);
}

.quiz-btn {
  background: var(--accent);
  color: white;
  border: none;
  padding: 0.55rem 1.5rem;
  border-radius: var(--radius-sm);
  font-size: 0.88rem;
  font-weight: 600;
  cursor: pointer;
  margin-top: 0.75rem;
  transition: all var(--transition);
}

.quiz-btn:hover { background: var(--accent-light); }

.quiz-btn:disabled {
  opacity: 0.5;
  cursor: not-allowed;
}

.quiz-feedback {
  margin-top: 1rem;
  padding: 0.75rem 1rem;
  border-radius: var(--radius-sm);
  font-size: 0.88rem;
  display: none;
}

.quiz-feedback.show { display: block; }

.quiz-feedback.correct {
  background: var(--green-dim);
  color: var(--green);
  border: 1px solid rgba(52, 211, 153, 0.3);
}

.quiz-feedback.incorrect {
  background: rgba(248, 113, 113, 0.1);
  color: var(--red);
  border: 1px solid rgba(248, 113, 113, 0.3);
}

/* --- Lesson Navigation (prev/next) --- */
.lesson-nav {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  margin-top: 3rem;
  padding-top: 1.5rem;
  border-top: 1px solid var(--border);
}

.lesson-nav-btn {
  display: flex;
  flex-direction: column;
  gap: 0.2rem;
  padding: 0.85rem 1.25rem;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  text-decoration: none;
  color: inherit;
  transition: all var(--transition);
  max-width: 48%;
}

.lesson-nav-btn:hover {
  border-color: var(--accent);
  background: var(--surface2);
}

.lesson-nav-btn .direction {
  font-size: 0.75rem;
  color: var(--text-dim);
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

.lesson-nav-btn .title {
  font-size: 0.9rem;
  font-weight: 500;
  color: var(--text);
}

.lesson-nav-btn.next { text-align: right; margin-left: auto; }

/* --- Mark Complete Button --- */
.btn-complete {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  padding: 0.6rem 1.25rem;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  color: var(--text-muted);
  font-size: 0.88rem;
  font-weight: 500;
  cursor: pointer;
  transition: all var(--transition);
  margin-top: 2rem;
}

.btn-complete:hover {
  border-color: var(--green);
  color: var(--green);
}

.btn-complete.completed {
  background: var(--green-dim);
  border-color: rgba(52, 211, 153, 0.3);
  color: var(--green);
}

/* --- Coming Soon / Empty State --- */
.empty-state {
  text-align: center;
  padding: 4rem 2rem;
  color: var(--text-muted);
}

.empty-state svg {
  width: 64px;
  height: 64px;
  color: var(--text-dim);
  margin-bottom: 1rem;
}

.empty-state h3 {
  font-size: 1.25rem;
  color: var(--text);
  margin-bottom: 0.5rem;
}

.empty-state p {
  font-size: 0.9rem;
  max-width: 400px;
  margin: 0 auto;
}

/* --- Footer --- */
.footer {
  text-align: center;
  padding: 2rem;
  color: var(--text-dim);
  font-size: 0.78rem;
  border-top: 1px solid var(--border);
}

.footer a { color: var(--text-muted); }

/* ==========================================================================
   Responsive
   ========================================================================== */

@media (max-width: 1024px) {
  .sidebar {
    transform: translateX(-100%);
  }

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

  .sidebar-overlay.open { display: block; }

  .main { margin-left: 0; }

  .btn-menu { display: flex; }
}

@media (max-width: 768px) {
  .hero-home { padding: 2.5rem 1.25rem 2rem; }
  .hero-home h1 { font-size: 1.8rem; }
  .hero-stats { gap: 1.5rem; }
  .section { padding: 2rem 1.25rem; }
  .course-grid { grid-template-columns: 1fr; }
  .course-header { padding: 2rem 1.25rem; }
  .course-header h1 { font-size: 1.5rem; }
  .course-content { padding: 1.5rem 1.25rem; }
  .lesson-content { padding: 1.5rem 1.25rem; }
  .lesson-content h1 { font-size: 1.4rem; }
  .lesson-nav { flex-direction: column; }
  .lesson-nav-btn { max-width: 100%; }
  .lesson-nav-btn.next { text-align: left; }
  .topbar-nav { display: none; }
  .topbar-progress-bar { width: 50px; }
}

@media (max-width: 480px) {
  :root { --topbar-height: 52px; }
  .hero-home h1 { font-size: 1.5rem; }
  .hero-stat .value { font-size: 1.5rem; }
  .code-block pre { font-size: 0.78rem; padding: 0.75rem; }
}