:root {
  --bg: #090815;
  --panel: #111123;
  --panel-2: #18172d;
  --ink: #f3f4ff;
  --muted: #9ca2ba;
  --cyan: #52e2f2;
  --amber: #ffca61;
  --line: rgba(255, 255, 255, 0.12);
  color-scheme: dark;
  font-family: "Manrope", "Segoe UI", sans-serif;
}

* { box-sizing: border-box; }

body {
  margin: 0;
  min-height: 100vh;
  color: var(--ink);
  background:
    radial-gradient(circle at 75% -10%, rgba(78, 84, 255, 0.25), transparent 34rem),
    linear-gradient(135deg, var(--bg), #0b1020 70%, #111022);
}

a { color: inherit; }

.site-header {
  min-height: 72px;
  padding: 0 5vw;
  display: flex;
  align-items: center;
  justify-content: space-between;
  border-bottom: 1px solid var(--line);
  background: rgba(9, 8, 21, 0.78);
  backdrop-filter: blur(18px);
  position: sticky;
  top: 0;
  z-index: 20;
}

.site-header nav { display: flex; align-items: center; gap: 1rem; color: var(--muted); }
.site-header form { margin: 0; }
.brand { font: 800 1rem/1 "JetBrains Mono", monospace; letter-spacing: 0.13em; text-decoration: none; }
.brand span { color: var(--cyan); }
.link-button { padding: 0; color: var(--cyan); background: none; border: 0; font: inherit; cursor: pointer; }

.hero {
  min-height: 55vh;
  padding: clamp(5rem, 12vw, 10rem) 8vw 5rem;
  display: grid;
  align-content: center;
  border-bottom: 1px solid var(--line);
}

.eyebrow { color: var(--cyan); font: 700 0.72rem/1.4 "JetBrains Mono", monospace; letter-spacing: 0.16em; text-transform: uppercase; }
h1 { max-width: 13ch; margin: 0.3rem 0 1rem; font-size: clamp(3rem, 9vw, 8.5rem); line-height: 0.9; letter-spacing: -0.065em; }
.hero-intro, .page-heading > p { max-width: 58rem; color: var(--muted); font-size: clamp(1.05rem, 2vw, 1.35rem); line-height: 1.65; }

.page-grid { display: grid; grid-template-columns: repeat(12, 1fr); gap: 1px; background: var(--line); border-bottom: 1px solid var(--line); }
.page-card, .empty-state { grid-column: span 6; min-height: 280px; padding: clamp(2rem, 5vw, 4.5rem); background: var(--panel); text-decoration: none; transition: background 180ms ease, transform 180ms ease; }
.page-card:hover { position: relative; background: var(--panel-2); transform: translateY(-3px); }
.page-card::before { content: ""; display: block; width: 56px; height: 3px; margin-bottom: 2.5rem; background: var(--accent, var(--amber)); }
.page-card h2, .empty-state h2 { margin: 0 0 1rem; font-size: clamp(1.6rem, 3vw, 2.6rem); }
.page-card p, .empty-state p { max-width: 42rem; color: var(--muted); line-height: 1.65; }
.card-index, .card-meta { font: 600 0.75rem/1.4 "JetBrains Mono", monospace; color: var(--cyan) !important; }

.content-shell, .lesson-shell { width: min(1180px, 90vw); margin: 0 auto; padding: 4rem 0 8rem; }
.lesson-shell { width: min(820px, 90vw); }
.breadcrumb { display: inline-block; margin-bottom: 5rem; color: var(--muted); text-decoration: none; }
.page-heading { padding-bottom: 4rem; border-bottom: 1px solid var(--line); }
.page-heading h1 { font-size: clamp(3rem, 7vw, 6.5rem); }
.content-shell .page-grid { margin-top: 3rem; border: 1px solid var(--line); }

.lesson-list { margin: 3rem 0 0; padding: 0; list-style: none; border-top: 1px solid var(--line); }
.lesson-list a { display: grid; grid-template-columns: 4rem 1fr auto; gap: 1rem; padding: 1.5rem 0; align-items: center; border-bottom: 1px solid var(--line); text-decoration: none; }
.lesson-list span, .lesson-list small { color: var(--muted); font-family: "JetBrains Mono", monospace; }

.lesson-body { padding-top: 3rem; font-size: 1.08rem; line-height: 1.8; }
.lesson-body h2, .lesson-body h3 { margin-top: 3rem; line-height: 1.2; }
.callout { margin: 2rem 0; padding: 1.5rem 1.75rem; border-left: 4px solid var(--cyan); background: rgba(82, 226, 242, 0.07); }
.callout-warning { border-color: var(--amber); background: rgba(255, 202, 97, 0.07); }
.callout-exam { border-color: #ff6d91; background: rgba(255, 109, 145, 0.07); }
.code-block { margin: 2rem 0; border: 1px solid var(--line); background: #060611; }
.code-block figcaption { padding: 0.7rem 1rem; color: var(--cyan); border-bottom: 1px solid var(--line); font: 600 0.75rem "JetBrains Mono", monospace; }
.code-block pre { margin: 0; padding: 1.5rem; overflow-x: auto; }

.auth-shell { min-height: calc(100vh - 72px); display: grid; place-items: center; padding: 2rem; }
.auth-card { width: min(460px, 100%); padding: clamp(2rem, 5vw, 4rem); border: 1px solid var(--line); background: var(--panel); }
.auth-card h1 { font-size: clamp(2rem, 6vw, 3.5rem); line-height: 1; }
.auth-card label { display: block; margin: 1.2rem 0 0.45rem; color: var(--muted); }
.auth-card input { width: 100%; padding: 0.9rem 1rem; color: var(--ink); border: 1px solid var(--line); background: #090916; font: inherit; }
.auth-card button[type="submit"] { width: 100%; margin-top: 1.5rem; padding: 1rem; border: 0; color: #071014; background: var(--cyan); font-weight: 800; cursor: pointer; }
.form-error { color: #ff8ca5; }

@media (max-width: 720px) {
  .site-header { padding: 0 1.25rem; }
  .site-header nav span { display: none; }
  .hero { min-height: 45vh; padding-inline: 1.25rem; }
  .page-card, .empty-state { grid-column: span 12; min-height: 230px; padding: 2rem 1.25rem; }
  .content-shell, .lesson-shell { width: min(100% - 2.5rem, 820px); padding-top: 2rem; }
  .breadcrumb { margin-bottom: 3rem; }
  .lesson-list a { grid-template-columns: 2.5rem 1fr; }
  .lesson-list small { grid-column: 2; }
}