/* ============================================================
   CodeHub — Global Stylesheet
   Beautiful, accessible, responsive, light/dark mode.
   No frameworks, no dependencies. Pure CSS.
   ============================================================ */

:root {
  --bg: #f7f9fc;
  --bg-alt: #ffffff;
  --surface: #ffffff;
  --surface-2: #eef2f8;
  --text: #0f172a;
  --text-muted: #475569;
  --border: #d8e0ec;
  --primary: #4f46e5;
  --primary-strong: #4338ca;
  --primary-soft: #eef2ff;
  --accent: #06b6d4;
  --accent-2: #8b5cf6;
  --success: #16a34a;
  --warning: #d97706;
  --code-bg: #0f172a;
  --code-text: #e2e8f0;
  --shadow: 0 10px 30px -12px rgba(15, 23, 42, 0.25);
  --shadow-sm: 0 2px 8px -2px rgba(15, 23, 42, 0.15);
  --radius: 16px;
  --radius-sm: 10px;
  --maxw: 1100px;
  --font: "Segoe UI", system-ui, -apple-system, Roboto, Helvetica, Arial, sans-serif;
  --mono: "SFMono-Regular", Consolas, "Liberation Mono", Menlo, monospace;
}

[data-theme="dark"] {
  --bg: #0b1120;
  --bg-alt: #0f172a;
  --surface: #111c33;
  --surface-2: #16233f;
  --text: #e2e8f0;
  --text-muted: #94a3b8;
  --border: #243049;
  --primary: #818cf8;
  --primary-strong: #a5b4fc;
  --primary-soft: #1e293b;
  --accent: #22d3ee;
  --accent-2: #a78bfa;
  --code-bg: #060b16;
  --code-text: #e2e8f0;
  --shadow: 0 10px 30px -12px rgba(0, 0, 0, 0.6);
  --shadow-sm: 0 2px 8px -2px rgba(0, 0, 0, 0.5);
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  font-family: var(--font);
  background: var(--bg);
  color: var(--text);
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
  transition: background 0.3s ease, color 0.3s ease;
}
img { max-width: 100%; display: block; }
a { color: var(--primary); text-decoration: none; }
a:hover { text-decoration: underline; }

/* Skip link (accessibility) */
.skip-link {
  position: absolute;
  left: -999px;
  top: 0;
  background: var(--primary);
  color: #fff;
  padding: 10px 16px;
  border-radius: 0 0 8px 0;
  z-index: 1000;
}
.skip-link:focus { left: 0; }

.container { width: 100%; max-width: var(--maxw); margin: 0 auto; padding: 0 20px; }

/* Header / Nav */
.site-header {
  position: sticky; top: 0; z-index: 50;
  background: color-mix(in srgb, var(--surface) 88%, transparent);
  backdrop-filter: blur(10px);
  border-bottom: 1px solid var(--border);
}
.nav { display: flex; align-items: center; justify-content: space-between; height: 64px; }
.brand { display: flex; align-items: center; gap: 10px; font-weight: 800; font-size: 1.25rem; color: var(--text); }
.brand:hover { text-decoration: none; }
.brand .logo {
  width: 34px; height: 34px; border-radius: 9px;
  background: linear-gradient(135deg, var(--primary), var(--accent-2));
  display: grid; place-items: center; color: #fff; font-weight: 900; font-size: 1.1rem;
}
.nav-links { display: flex; gap: 6px; align-items: center; list-style: none; margin: 0; padding: 0; }
.nav-links a {
  color: var(--text-muted); font-weight: 600; padding: 8px 12px;
  border-radius: 8px; transition: background 0.2s, color 0.2s;
}
.nav-links a:hover, .nav-links a:focus { background: var(--surface-2); color: var(--text); text-decoration: none; }
.nav-links a.active { color: var(--primary); }

.theme-toggle {
  border: 1px solid var(--border); background: var(--surface); color: var(--text);
  width: 42px; height: 42px; border-radius: 10px; cursor: pointer;
  font-size: 1.1rem; display: grid; place-items: center;
  transition: background 0.2s, transform 0.1s;
}
.theme-toggle:hover { background: var(--surface-2); }
.theme-toggle:active { transform: scale(0.94); }
.nav-toggle {
  display: none; background: var(--surface); border: 1px solid var(--border);
  color: var(--text); width: 42px; height: 42px; border-radius: 10px;
  font-size: 1.2rem; cursor: pointer;
}

/* Buttons */
.btn {
  display: inline-flex; align-items: center; gap: 8px;
  padding: 12px 22px; border-radius: 12px;
  font-weight: 700; font-size: 1rem; cursor: pointer;
  border: 1px solid transparent;
  transition: transform 0.12s ease, box-shadow 0.2s ease, background 0.2s;
}
.btn-primary {
  background: linear-gradient(135deg, var(--primary), var(--accent-2));
  color: #fff; box-shadow: var(--shadow-sm);
}
.btn-primary:hover { transform: translateY(-2px); text-decoration: none; box-shadow: var(--shadow); }
.btn-ghost { background: var(--surface); border-color: var(--border); color: var(--text); }
.btn-ghost:hover { background: var(--surface-2); text-decoration: none; }

/* Hero */
.hero {
  position: relative; overflow: hidden; padding: 90px 0 70px; text-align: center;
  background:
    radial-gradient(60% 60% at 20% 10%, color-mix(in srgb, var(--primary) 22%, transparent), transparent 70%),
    radial-gradient(50% 50% at 85% 20%, color-mix(in srgb, var(--accent) 22%, transparent), transparent 70%),
    var(--bg-alt);
}
.hero h1 {
  font-size: clamp(2.2rem, 6vw, 3.6rem); line-height: 1.1;
  margin: 0 0 18px; letter-spacing: -0.02em; font-weight: 900;
}
.hero h1 .grad {
  background: linear-gradient(120deg, var(--primary), var(--accent), var(--accent-2));
  -webkit-background-clip: text; background-clip: text; color: transparent;
}
.hero p {
  font-size: clamp(1rem, 2.2vw, 1.25rem); color: var(--text-muted);
  max-width: 680px; margin: 0 auto 30px;
}
.hero-cta { display: flex; gap: 14px; justify-content: center; flex-wrap: wrap; }
.hero-chips { display: flex; gap: 10px; justify-content: center; flex-wrap: wrap; margin-top: 38px; }
.chip {
  background: var(--surface); border: 1px solid var(--border); border-radius: 999px;
  padding: 8px 16px; font-size: 0.9rem; font-weight: 600; color: var(--text-muted);
  box-shadow: var(--shadow-sm);
}

/* Sections */
section { padding: 64px 0; }
.section-head { text-align: center; margin-bottom: 40px; }
.section-head h2 { font-size: clamp(1.6rem, 4vw, 2.4rem); margin: 0 0 10px; font-weight: 800; letter-spacing: -0.01em; }
.section-head p { color: var(--text-muted); max-width: 640px; margin: 0 auto; }

/* Cards grid */
.grid { display: grid; gap: 22px; grid-template-columns: repeat(auto-fill, minmax(260px, 1fr)); }
.card {
  background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius);
  padding: 24px; box-shadow: var(--shadow-sm);
  transition: transform 0.15s ease, box-shadow 0.2s ease, border-color 0.2s;
  display: flex; flex-direction: column; gap: 10px;
}
.card:hover {
  transform: translateY(-4px); box-shadow: var(--shadow);
  border-color: color-mix(in srgb, var(--primary) 40%, var(--border));
}
.card .icon {
  width: 48px; height: 48px; border-radius: 12px; display: grid; place-items: center;
  font-size: 1.4rem; background: var(--primary-soft); margin-bottom: 4px;
}
.card h3 { margin: 0; font-size: 1.2rem; }
.card p { margin: 0; color: var(--text-muted); font-size: 0.95rem; }
.card .tag {
  align-self: flex-start; font-size: 0.75rem; font-weight: 700;
  padding: 4px 10px; border-radius: 999px;
  background: var(--surface-2); color: var(--text-muted); margin-top: auto;
}

/* Feature list */
.features { display: grid; gap: 22px; grid-template-columns: repeat(auto-fit, minmax(240px, 1fr)); }
.feature { background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius); padding: 26px; }
.feature .icon {
  font-size: 1.8rem; margin-bottom: 12px; width: 52px; height: 52px;
  border-radius: 14px; display: grid; place-items: center; background: var(--primary-soft);
}
.feature h3 { margin: 0 0 8px; font-size: 1.15rem; }
.feature p { margin: 0; color: var(--text-muted); font-size: 0.95rem; }

/* Breadcrumb */
.breadcrumb { font-size: 0.9rem; color: var(--text-muted); padding: 18px 0 0; }
.breadcrumb a { color: var(--text-muted); }
.breadcrumb span { margin: 0 6px; }

/* Tutorial layout */
.tutorial-layout { display: grid; grid-template-columns: 260px 1fr; gap: 40px; align-items: start; }
.toc {
  position: sticky; top: 84px; background: var(--surface);
  border: 1px solid var(--border); border-radius: var(--radius); padding: 18px;
}
.toc h4 { margin: 0 0 12px; font-size: 0.85rem; text-transform: uppercase; letter-spacing: 0.06em; color: var(--text-muted); }
.toc ul { list-style: none; margin: 0; padding: 0; }
.toc li { margin: 2px 0; }
.toc a { display: block; padding: 7px 10px; border-radius: 8px; color: var(--text-muted); font-size: 0.92rem; }
.toc a:hover, .toc a:focus { background: var(--surface-2); color: var(--text); text-decoration: none; }
.toc a.active { background: var(--primary-soft); color: var(--primary); font-weight: 700; }

.lesson { background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius); padding: 30px; }
.lesson h2 { margin-top: 0; }
.lesson h3 { margin-top: 30px; }
.lesson p, .lesson li { color: var(--text); }
.lesson ul, .lesson ol { padding-left: 22px; }

/* Code block */
.codeblock { background: var(--code-bg); border-radius: var(--radius-sm); margin: 18px 0; overflow: hidden; border: 1px solid #1e293b; }
.codeblock .cb-head {
  display: flex; align-items: center; justify-content: space-between;
  padding: 8px 14px; background: #131f37; font-size: 0.8rem; color: #94a3b8; border-bottom: 1px solid #1e293b;
}
.codeblock .cb-lang { font-weight: 700; letter-spacing: 0.04em; }
.copy-btn {
  background: transparent; border: 1px solid #334155; color: #cbd5e1;
  border-radius: 6px; padding: 4px 10px; font-size: 0.75rem; cursor: pointer;
}
.copy-btn:hover { background: #1e293b; }
.codeblock pre {
  margin: 0; padding: 16px; overflow-x: auto; color: var(--code-text);
  font-family: var(--mono); font-size: 0.9rem; line-height: 1.55;
}

/* Callout */
.callout {
  display: flex; gap: 12px; padding: 14px 16px; border-radius: var(--radius-sm);
  border: 1px solid var(--border); background: var(--surface-2); margin: 18px 0; font-size: 0.95rem;
}
.callout .ico { font-size: 1.2rem; }
.callout.tip { border-color: color-mix(in srgb, var(--success) 40%, var(--border)); background: color-mix(in srgb, var(--success) 10%, var(--surface)); }
.callout.play { border-color: color-mix(in srgb, var(--accent) 45%, var(--border)); background: color-mix(in srgb, var(--accent) 10%, var(--surface)); }

/* Level Tabs */
.level-tabs {
  display: flex;
  gap: 6px;
  margin: 16px 0 24px;
  flex-wrap: wrap;
  border-bottom: 1px solid var(--border);
  padding-bottom: 8px;
}
.level-tab {
  padding: 10px 18px;
  border-radius: 999px;
  font-weight: 700;
  font-size: 0.875rem;
  cursor: pointer;
  background: var(--surface-2);
  border: 1px solid var(--border);
  color: var(--text-muted);
  transition: all 0.15s ease;
}
.level-tab:hover { background: var(--surface); color: var(--text); }
.level-tab.active {
  background: linear-gradient(135deg, var(--primary), var(--accent-2));
  border-color: transparent;
  color: #fff;
  box-shadow: var(--shadow-sm);
}
.level-tab:focus-visible { outline: 3px solid var(--primary); outline-offset: 2px; }

.level-panel { display: none; }
.level-panel.active { display: block; animation: fadeIn 0.2s ease; }
@keyframes fadeIn { from { opacity: 0; transform: translateY(4px); } to { opacity: 1; transform: none; } }

@media (prefers-reduced-motion: reduce) {
  .level-panel.active { animation: none; }
}

/* Footer */
.site-footer { background: var(--bg-alt); border-top: 1px solid var(--border); padding: 48px 0 28px; margin-top: 40px; }
.footer-grid { display: grid; grid-template-columns: 1.8fr repeat(4, 1fr); gap: 30px; }
.footer-grid h4 { font-size: 0.85rem; text-transform: uppercase; letter-spacing: 0.06em; color: var(--text-muted); margin: 0 0 12px; }
.footer-grid ul { list-style: none; padding: 0; margin: 0; }
.footer-grid li { margin: 6px 0; }
.footer-grid a { color: var(--text-muted); }
.footer-bottom {
  text-align: center; color: var(--text-muted); font-size: 0.875rem;
  margin-top: 30px; padding-top: 20px; border-top: 1px solid var(--border);
}

/* Stats */
.stats { display: flex; gap: 30px; justify-content: center; flex-wrap: wrap; margin-top: 10px; }
.stat { text-align: center; }
.stat .num { font-size: 2rem; font-weight: 900; background: linear-gradient(120deg, var(--primary), var(--accent)); -webkit-background-clip: text; background-clip: text; color: transparent; }
.stat .lbl { color: var(--text-muted); font-size: 0.9rem; }

/* a11y helpers */
:focus-visible { outline: 3px solid var(--primary); outline-offset: 2px; border-radius: 4px; }
.visually-hidden {
  position: absolute !important; width: 1px; height: 1px; padding: 0; margin: -1px;
  overflow: hidden; clip: rect(0,0,0,0); white-space: nowrap; border: 0;
}

/* Responsive */
@media (max-width: 860px) {
  .tutorial-layout { grid-template-columns: 1fr; }
  .toc { position: static; }
  .footer-grid { grid-template-columns: 1fr 1fr 1fr; }
  .hero-terminal { font-size: 0.85rem; }
  .hero-terminal .ht-body { min-height: 104px; padding: 14px; }
  .nav-links {
    position: absolute; top: 64px; left: 0; right: 0;
    flex-direction: column; background: var(--surface);
    border-bottom: 1px solid var(--border); padding: 12px; gap: 4px; display: none;
  }
  .nav-links.open { display: flex; }
  .nav-toggle { display: grid; place-items: center; }
}
@media (max-width: 520px) {
  .footer-grid { grid-template-columns: 1fr 1fr; }
  .lesson { padding: 20px; }
  .hero { padding: 70px 0 50px; }
  .hero-terminal { font-size: 0.78rem; margin-top: 24px; }
  .hero-terminal .ht-body { min-height: 92px; }
  .hero-chips .chip { padding: 6px 12px; font-size: 0.8rem; }
  .btn { padding: 11px 18px; font-size: 0.95rem; }
}
/* Extra small phones */
@media (max-width: 380px) {
  .footer-grid { grid-template-columns: 1fr; }
  .hero-terminal .ht-body { font-size: 0.72rem; }
}

/* Reduced motion */
@media (prefers-reduced-motion: reduce) {
  * { scroll-behavior: auto !important; transition: none !important; animation: none !important; }
}

/* ============================================================
   CodeHub — Animations & Motion (added)
   Hero animated background, typewriter terminal, scroll-reveal,
   floating particles, micro-interactions. Respects reduced-motion.
   ============================================================ */

/* Animated hero background (slow drifting gradient blobs) */
.hero::before,
.hero::after {
  content: "";
  position: absolute;
  border-radius: 50%;
  filter: blur(60px);
  opacity: 0.55;
  pointer-events: none;
  z-index: 0;
}
.hero::before {
  width: 420px; height: 420px;
  background: radial-gradient(circle at 30% 30%, var(--primary), transparent 70%);
  top: -120px; left: -80px;
  animation: heroDrift 18s ease-in-out infinite alternate;
}
.hero::after {
  width: 380px; height: 380px;
  background: radial-gradient(circle at 70% 70%, var(--accent-2), transparent 70%);
  bottom: -140px; right: -60px;
  animation: heroDrift2 22s ease-in-out infinite alternate;
}
.hero .container { position: relative; z-index: 1; }
@keyframes heroDrift {
  0%   { transform: translate(0, 0) scale(1); }
  100% { transform: translate(120px, 60px) scale(1.15); }
}
@keyframes heroDrift2 {
  0%   { transform: translate(0, 0) scale(1.1); }
  100% { transform: translate(-100px, -50px) scale(0.9); }
}

/* Floating code particles */
.hero-particles {
  position: absolute; inset: 0; overflow: hidden; pointer-events: none; z-index: 0;
}
.hero-particles span {
  position: absolute; bottom: -40px;
  font-family: var(--mono); font-size: 0.9rem; font-weight: 700;
  color: color-mix(in srgb, var(--primary) 55%, var(--text));
  opacity: 0; white-space: nowrap;
  animation: floatUp linear infinite;
}
@keyframes floatUp {
  0%   { transform: translateY(0) rotate(0deg); opacity: 0; }
  10%  { opacity: 0.5; }
  90%  { opacity: 0.5; }
  100% { transform: translateY(-520px) rotate(12deg); opacity: 0; }
}

/* Typewriter terminal in hero */
.hero-terminal {
  max-width: 560px; margin: 34px auto 0; text-align: left;
  background: #060b16; border: 1px solid #1e293b; border-radius: 14px;
  box-shadow: var(--shadow); overflow: hidden; font-family: var(--mono);
}
.hero-terminal .ht-head {
  display: flex; align-items: center; gap: 7px;
  padding: 10px 14px; background: #0f172a; border-bottom: 1px solid #1e293b;
}
.hero-terminal .dot { width: 12px; height: 12px; border-radius: 50%; }
.hero-terminal .dot.r { background: #ff5f56; }
.hero-terminal .dot.y { background: #ffbd2e; }
.hero-terminal .dot.g { background: #27c93f; }
.hero-terminal .ht-title { margin-left: 8px; color: #94a3b8; font-size: 0.78rem; }
.hero-terminal .ht-body {
  padding: 16px 18px; min-height: 118px; color: #e2e8f0; font-size: 0.92rem; line-height: 1.7;
}
.hero-terminal .ht-line { white-space: pre-wrap; }
.hero-terminal .kw { color: #c084fc; }
.hero-terminal .fn { color: #38bdf8; }
.hero-terminal .str { color: #34d399; }
.hero-terminal .cm { color: #64748b; }
.hero-terminal .cursor {
  display: inline-block; width: 9px; height: 1.05em; vertical-align: text-bottom;
  background: #38bdf8; margin-left: 2px; animation: blink 1s steps(2) infinite;
}
@keyframes blink { 0%, 50% { opacity: 1; } 50.01%, 100% { opacity: 0; } }

/* Scroll-reveal */
.reveal { opacity: 0; transform: translateY(24px); transition: opacity 0.6s ease, transform 0.6s ease; }
.reveal.in { opacity: 1; transform: none; }
.reveal-delay-1 { transition-delay: 0.08s; }
.reveal-delay-2 { transition-delay: 0.16s; }
.reveal-delay-3 { transition-delay: 0.24s; }
.reveal-delay-4 { transition-delay: 0.32s; }
@media (prefers-reduced-motion: reduce) {
  .hero::before, .hero::after, .hero-particles span, .hero-terminal .cursor { animation: none; }
  .reveal { opacity: 1; transform: none; transition: none; }
}

/* Micro-interaction: magnetic-ish button pulse on load */
@keyframes popIn { from { transform: scale(0.96); opacity: 0; } to { transform: scale(1); opacity: 1; } }
.hero-cta { animation: popIn 0.6s ease both; }

/* Card hover lift already exists; add subtle glow */
.card:hover, .feature:hover {
  box-shadow: 0 18px 40px -16px color-mix(in srgb, var(--primary) 55%, transparent);
}

/* Gradient text shimmer for hero title */
.hero h1 .grad { background-size: 200% auto; animation: shimmer 6s linear infinite; }
@keyframes shimmer { to { background-position: 200% center; } }
@media (prefers-reduced-motion: reduce) {
  .hero h1 .grad { animation: none; }
}