:root {
  --bg: #0a0a10;
  --card: #111118;
  --border: #1c1c2a;
  --text: #c4c4d8;
  --text-muted: #60607a;
  --accent: #4a90d9;
  --accent-dim: #1a2f48;
  --heading: #f0f0f8;
}

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

body {
  background: var(--bg);
  color: var(--text);
  font-family: 'Segoe UI', system-ui, -apple-system, sans-serif;
  font-size: 17px;
  line-height: 1.75;
}

.container {
  max-width: 720px;
  margin: 0 auto;
  padding: 0 24px 64px;
}

/* ── Progress bar ── */
.progress-bar { background: var(--border); height: 3px; width: 100%; }
.progress-fill { background: var(--accent); height: 3px; transition: width 0.3s; }

/* ── Header ── */
.site-header { padding: 32px 0 24px; margin-bottom: 40px; border-bottom: 1px solid var(--border); }
.lesson-label {
  font-size: 12px;
  text-transform: uppercase;
  letter-spacing: 0.12em;
  color: var(--accent);
  margin-bottom: 10px;
}
h1 { font-size: 2rem; font-weight: 700; color: var(--heading); line-height: 1.2; }
.subtitle { margin-top: 10px; color: var(--text-muted); font-size: 15px; }

/* ── Body text ── */
h2 {
  font-size: 1.15rem;
  font-weight: 600;
  color: var(--heading);
  margin: 40px 0 12px;
  padding-top: 32px;
  border-top: 1px solid var(--border);
}
h2:first-of-type { border-top: none; padding-top: 0; margin-top: 0; }
p { margin-bottom: 16px; }
ul, ol { padding-left: 24px; margin-bottom: 16px; }
li { margin-bottom: 8px; }
strong { color: var(--heading); font-weight: 600; }

/* ── Callout ── */
.callout {
  background: var(--accent-dim);
  border-left: 3px solid var(--accent);
  border-radius: 4px;
  padding: 16px 20px;
  margin: 24px 0;
}
.callout p:last-child { margin-bottom: 0; }
.callout.warn { background: #2a1a10; border-color: #c87941; }

/* ── Table ── */
table { width: 100%; border-collapse: collapse; margin: 16px 0 24px; }
th {
  text-align: left;
  padding: 10px 14px;
  background: var(--border);
  color: var(--heading);
  font-size: 13px;
  text-transform: uppercase;
  letter-spacing: 0.05em;
}
td { padding: 10px 14px; border-bottom: 1px solid var(--border); }
tr:last-child td { border-bottom: none; }

/* ── Navigation ── */
.lesson-nav {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-top: 64px;
  padding-top: 24px;
  border-top: 1px solid var(--border);
  gap: 12px;
}
.btn {
  display: inline-block;
  padding: 12px 24px;
  border-radius: 6px;
  font-size: 14px;
  font-weight: 600;
  text-decoration: none;
  cursor: pointer;
  transition: background-color 0.2s ease, color 0.2s ease, border-color 0.2s ease;
}
.btn-primary { background: var(--accent); color: #fff; }
.btn-primary:hover { background: #5aa0e9; }
.btn-ghost { background: transparent; color: var(--text-muted); border: 1px solid var(--border); }
.btn-ghost:hover { color: var(--text); border-color: var(--text); }
.nav-spacer { flex: 1; }

/* ── Index page ── */
.welcome { margin-bottom: 40px; }
.welcome p { font-size: 18px; line-height: 1.7; }
.lessons-heading {
  font-size: 12px;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--text-muted);
  margin-bottom: 16px;
}
.lesson-list { list-style: none; padding: 0; }
.lesson-item {
  display: flex;
  align-items: flex-start;
  gap: 16px;
  padding: 18px 0;
  border-bottom: 1px solid var(--border);
}
.lesson-item:last-child { border-bottom: none; }
.lesson-num {
  width: 36px;
  height: 36px;
  background: var(--accent-dim);
  color: var(--accent);
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 13px;
  font-weight: 700;
  flex-shrink: 0;
  margin-top: 2px;
}
.lesson-item-title { font-size: 16px; font-weight: 600; color: var(--heading); }
.lesson-item-desc { font-size: 14px; color: var(--text-muted); margin-top: 3px; }
.start-cta { display: flex; justify-content: center; margin-top: 40px; }
.btn-large { padding: 16px 40px; font-size: 16px; border-radius: 8px; }

/* ── Footer ── */
.site-footer {
  margin-top: 48px;
  padding-top: 24px;
  border-top: 1px solid var(--border);
  font-size: 13px;
  color: var(--text-muted);
}

/* ── Video embed ── */
.video-wrap {
  position: relative;
  padding-bottom: 56.25%;
  height: 0;
  overflow: hidden;
  margin: 24px 0;
  border-radius: 6px;
  background: #000;
}
.video-wrap iframe {
  position: absolute;
  top: 0; left: 0;
  width: 100%; height: 100%;
  border: 0;
}
.video-label {
  font-size: 12px;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--text-muted);
  margin-bottom: 8px;
}

/* ── Mobile ── */
@media (max-width: 600px) {
  h1 { font-size: 1.5rem; }
  .lesson-nav { flex-direction: column; }
  .btn { text-align: center; width: 100%; }
  .nav-spacer { display: none; }
}