:root {
  --bg: #0a0a0f;
  --bg2: #12121a;
  --bg3: #1a1a2e;
  --accent: #00d4ff;
  --accent2: #7b61ff;
  --text: #e0e0e8;
  --text2: #8888a0;
  --green: #00e676;
  --red: #ff5252;
  --radius: 12px;
  --max-w: 1100px;
}

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

html { scroll-behavior: smooth; }

body {
  font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.7;
  -webkit-font-smoothing: antialiased;
}

a { color: var(--accent); text-decoration: none; transition: opacity .2s; }
a:hover { opacity: .8; }

.container { max-width: var(--max-w); margin: 0 auto; padding: 0 24px; }

/* NAV */
nav {
  position: fixed; top: 0; left: 0; right: 0; z-index: 100;
  background: rgba(10,10,15,.85); backdrop-filter: blur(20px);
  border-bottom: 1px solid rgba(255,255,255,.06);
  padding: 16px 0;
}
nav .container { display: flex; justify-content: space-between; align-items: center; }
.logo { font-weight: 700; font-size: 1.1rem; letter-spacing: -.02em; }
.logo span { color: var(--accent); }
nav ul { list-style: none; display: flex; gap: 28px; }
nav ul a { color: var(--text2); font-size: .9rem; font-weight: 500; }
nav ul a:hover { color: var(--text); }

/* HERO */
.hero {
  padding: 160px 0 100px;
  text-align: center;
  background: radial-gradient(ellipse at 50% 0%, rgba(0,212,255,.08) 0%, transparent 60%);
}
.hero .badge {
  display: inline-block; padding: 6px 16px; border-radius: 20px;
  background: rgba(0,212,255,.1); border: 1px solid rgba(0,212,255,.2);
  color: var(--accent); font-size: .8rem; font-weight: 600;
  margin-bottom: 24px; letter-spacing: .04em; text-transform: uppercase;
}
.hero h1 {
  font-size: clamp(2.2rem, 5vw, 3.5rem); font-weight: 800;
  line-height: 1.15; letter-spacing: -.03em; max-width: 800px; margin: 0 auto 20px;
}
.hero h1 em { font-style: normal; color: var(--accent); }
.hero p { font-size: 1.15rem; color: var(--text2); max-width: 600px; margin: 0 auto 36px; }

.btn {
  display: inline-block; padding: 14px 32px; border-radius: 8px;
  font-weight: 600; font-size: 1rem; cursor: pointer; border: none; transition: all .2s;
}
.btn-primary { background: var(--accent); color: var(--bg); }
.btn-primary:hover { background: #33ddff; opacity: 1; transform: translateY(-1px); }
.btn-ghost {
  background: transparent; color: var(--text);
  border: 1px solid rgba(255,255,255,.15); margin-left: 12px;
}
.btn-ghost:hover { border-color: var(--accent); color: var(--accent); opacity: 1; }

/* STATS BAR */
.stats {
  display: flex; justify-content: center; gap: 48px;
  padding: 48px 0; border-top: 1px solid rgba(255,255,255,.06);
}
.stat { text-align: center; }
.stat .num { font-size: 2rem; font-weight: 800; color: var(--accent); }
.stat .label { font-size: .85rem; color: var(--text2); margin-top: 4px; }

/* SECTIONS */
section { padding: 80px 0; }
section h2 {
  font-size: 2rem; font-weight: 800; letter-spacing: -.02em;
  margin-bottom: 16px;
}
section .subtitle { color: var(--text2); font-size: 1.1rem; margin-bottom: 48px; }

/* BOOK MOCKUP */
.book-mockup {
  text-align: center;
  margin-bottom: 40px;
}
.book-mockup img {
  max-width: 100%;
  width: min(420px, 100%);
  height: auto;
  border-radius: var(--radius);
  display: block;
  margin: 0 auto;
  box-shadow: 0 20px 40px rgba(0,0,0,.4);
}

/* CARD GRID */
.grid { display: grid; gap: 20px; }
.grid-2 { grid-template-columns: repeat(auto-fit, minmax(320px, 1fr)); }
.grid-3 { grid-template-columns: repeat(auto-fit, minmax(280px, 1fr)); }
.grid-4 { grid-template-columns: repeat(auto-fit, minmax(220px, 1fr)); }

.card {
  background: var(--bg2); border: 1px solid rgba(255,255,255,.06);
  border-radius: var(--radius); padding: 28px; transition: all .25s;
}
.card:hover { border-color: rgba(0,212,255,.2); transform: translateY(-2px); }
.card .icon { font-size: 2rem; margin-bottom: 16px; }
.card h3 { font-size: 1.15rem; font-weight: 700; margin-bottom: 8px; }
.card p { color: var(--text2); font-size: .95rem; }
.card .tag {
  display: inline-block; padding: 3px 10px; border-radius: 6px;
  font-size: .75rem; font-weight: 600; margin-top: 12px;
}
.tag-free { background: rgba(0,230,118,.12); color: var(--green); }
.tag-new { background: rgba(123,97,255,.12); color: var(--accent2); }

/* CHAPTERS */
.chapter-card { position: relative; overflow: hidden; }
.chapter-card .ch-num {
  position: absolute; top: 16px; right: 20px;
  font-size: 3rem; font-weight: 900; color: rgba(255,255,255,.04);
  line-height: 1;
}
.chapter-card h3 a { color: var(--text); }
.chapter-card h3 a:hover { color: var(--accent); }
.chapter-card .resources { margin-top: 16px; display: flex; gap: 8px; flex-wrap: wrap; }
.res-tag {
  padding: 4px 10px; border-radius: 6px; font-size: .75rem; font-weight: 600;
  background: var(--bg3); color: var(--text2); border: 1px solid rgba(255,255,255,.06);
}

/* WAITLIST */
.waitlist-section {
  background: linear-gradient(135deg, rgba(0,212,255,.06), rgba(123,97,255,.06));
  border-radius: var(--radius); padding: 60px 48px; text-align: center;
  border: 1px solid rgba(255,255,255,.06); margin: 40px 0;
}
.waitlist-form {
  display: flex; gap: 12px; max-width: 480px; margin: 28px auto 0;
  flex-wrap: wrap; justify-content: center;
}
.waitlist-form input {
  flex: 1; min-width: 240px; padding: 14px 18px; border-radius: 8px;
  border: 1px solid rgba(255,255,255,.12); background: var(--bg);
  color: var(--text); font-size: 1rem; outline: none;
}
.waitlist-form input:focus { border-color: var(--accent); }
.waitlist-form .btn { min-width: 140px; }

/* FOOTER */
footer {
  padding: 48px 0; border-top: 1px solid rgba(255,255,255,.06);
  text-align: center; color: var(--text2); font-size: .85rem;
}
footer .links { margin-bottom: 16px; }
footer .links a { margin: 0 16px; color: var(--text2); }
footer .links a:hover { color: var(--accent); }

/* CHAPTER PAGE */
.ch-hero {
  padding: 140px 0 60px;
  background: radial-gradient(ellipse at 50% 0%, rgba(123,97,255,.08) 0%, transparent 60%);
}
.ch-hero .back { color: var(--text2); font-size: .9rem; display: inline-block; margin-bottom: 20px; }
.ch-hero .back:hover { color: var(--accent); }
.ch-hero h1 { font-size: 2.4rem; font-weight: 800; margin-bottom: 12px; }
.ch-hero .ch-meta { color: var(--text2); }

.ch-content { padding: 60px 0; }
.ch-content h2 { font-size: 1.5rem; margin: 48px 0 16px; }
.ch-content h2:first-child { margin-top: 0; }
.ch-content p { margin-bottom: 16px; max-width: 720px; }
.ch-content ul { margin: 0 0 16px 24px; }
.ch-content li { margin-bottom: 8px; color: var(--text2); }

.code-block {
  background: var(--bg2); border: 1px solid rgba(255,255,255,.08);
  border-radius: var(--radius); padding: 24px; margin: 24px 0;
  overflow-x: auto;
}
.code-block code { font-family: 'JetBrains Mono', 'Fira Code', monospace; font-size: .9rem; line-height: 1.6; }

.colab-btn {
  display: inline-flex; align-items: center; gap: 8px;
  padding: 12px 24px; border-radius: 8px;
  background: rgba(0,230,118,.1); border: 1px solid rgba(0,230,118,.25);
  color: var(--green); font-weight: 600; font-size: .95rem; margin: 16px 0;
}
.colab-btn:hover { background: rgba(0,230,118,.18); opacity: 1; }

.resource-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(280px, 1fr)); gap: 16px; margin: 24px 0; }

@media (max-width: 640px) {
  .hero h1 { font-size: 1.8rem; }
  .stats { flex-direction: column; gap: 24px; }
  nav ul { gap: 16px; }
  .waitlist-section { padding: 40px 24px; }
  .btn-ghost { margin-left: 0; margin-top: 12px; }
  .hero .buttons { display: flex; flex-direction: column; align-items: center; }
}