:root {
  --bg: #0f1117;
  --surface: #1a1d27;
  --surface2: #22263a;
  --border: #2e3250;
  --accent: #6c8ef5;
  --accent2: #a78bfa;
  --green: #4ade80;
  --yellow: #fbbf24;
  --pink: #f472b6;
  --text: #e2e8f0;
  --muted: #8892b0;
  --sidebar-width: 280px;
}

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

body {
  font-family: 'Inter', -apple-system, sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.7;
  display: flex;
  min-height: 100vh;
}

/* ── Sidebar toggle ── */
body.sidebar-hidden .sidebar { transform: translateX(-100%); }
body.sidebar-hidden .main    { margin-left: 0; }

.sidebar {
  transition: transform 0.25s ease;
}
.main {
  transition: margin-left 0.25s ease;
}

.sidebar-toggle {
  background: none;
  border: 1px solid var(--border);
  border-radius: 6px;
  color: var(--muted);
  cursor: pointer;
  padding: 5px 7px;
  display: flex;
  align-items: center;
  transition: border-color 0.15s, color 0.15s;
}
.sidebar-toggle:hover { border-color: var(--accent); color: var(--text); }

/* ── Generate button ── */
.generate-btn {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  background: var(--accent);
  color: #fff;
  border: none;
  border-radius: 9px;
  padding: 12px 24px;
  font-size: 15px;
  font-weight: 600;
  cursor: pointer;
  transition: opacity 0.15s;
}
.generate-btn:hover { opacity: 0.88; }

/* ── Spinner ── */
.spinner {
  width: 36px; height: 36px;
  border: 3px solid var(--border);
  border-top-color: var(--accent);
  border-radius: 50%;
  margin: 0 auto;
  animation: spin 0.8s linear infinite;
}
@keyframes spin { to { transform: rotate(360deg); } }

/* ── Sidebar ── */
.sidebar {
  width: var(--sidebar-width);
  height: 100vh;
  background: var(--surface);
  border-right: 1px solid var(--border);
  position: fixed;
  top: 0; left: 0;
  z-index: 100;
  display: flex;
  flex-direction: column;
  overflow: hidden;
}
.sidebar-lessons {
  flex: 1;
  overflow-y: auto;
  padding-bottom: 8px;
}
.sidebar-footer {
  padding: 8px 20px;
  border-top: 1px solid var(--border);
  flex-shrink: 0;
}

.sidebar-logo {
  padding: 20px 20px 16px;
  border-bottom: 1px solid var(--border);
}
.sidebar-logo h1 {
  font-size: 18px;
  font-weight: 700;
  color: var(--accent);
  letter-spacing: -0.3px;
}
.sidebar-logo p {
  font-size: 11px;
  color: var(--muted);
  margin-top: 2px;
}

.phase-group { padding: 2px 0; }

.phase-label {
  display: flex;
  align-items: center;
  justify-content: space-between;
  font-size: 11px;
  font-weight: 700;
  color: var(--text);
  padding: 8px 12px 6px 14px;
  margin: 6px 8px 2px;
  background: var(--surface2);
  border: 1px solid var(--border);
  border-radius: 7px;
  letter-spacing: .2px;
}

.phase-label .gpu-badge {
  font-size: 9px;
  font-weight: 700;
  background: rgba(251,191,36,0.15);
  color: #fbbf24;
  border: 1px solid rgba(251,191,36,0.3);
  border-radius: 4px;
  padding: 1px 5px;
  letter-spacing: .3px;
  flex-shrink: 0;
}

.lesson-link {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 7px 20px;
  text-decoration: none;
  color: var(--muted);
  font-size: 13px;
  transition: all 0.15s;
  border-left: 2px solid transparent;
}
.lesson-link:hover { background: var(--surface2); color: var(--text); }
.lesson-link.active {
  color: var(--accent);
  border-left-color: var(--accent);
  background: rgba(108,142,245,0.08);
}
.lesson-link.done { color: var(--green); }
.lesson-link.done .status-dot { background: var(--green); }

.status-dot {
  width: 6px; height: 6px;
  border-radius: 50%;
  background: var(--border);
  flex-shrink: 0;
}
.lesson-link.active .status-dot { background: var(--accent); }

/* ── Main ── */
.main {
  margin-left: var(--sidebar-width);
  flex: 1;
  display: flex;
  flex-direction: column;
  min-height: 100vh;
}

.topbar {
  background: var(--surface);
  border-bottom: 1px solid var(--border);
  padding: 14px 220px 14px 40px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  position: sticky;
  top: 0;
  z-index: 50;
}
.topbar-breadcrumb {
  font-size: 13px;
  color: var(--muted);
}
.topbar-breadcrumb span { color: var(--text); font-weight: 500; }

.colab-btn {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  background: #f9ab00;
  color: #000;
  font-size: 13px;
  font-weight: 600;
  padding: 8px 16px;
  border-radius: 8px;
  text-decoration: none;
  transition: opacity 0.15s;
}
.colab-btn:hover { opacity: 0.88; }
.colab-btn svg { width: 16px; height: 16px; }

.colab-btn.dl {
  background: var(--surface2);
  color: var(--text);
  border: 1px solid var(--border);
}

/* ── Content ── */
.content {
  max-width: 100%;
  margin: 0;
  padding: 40px 48px 80px;
  width: 100%;
  box-sizing: border-box;
}

/* ── User widget (top-right) ── */
.user-widget {
  position: fixed;
  top: 12px;
  right: 20px;
  z-index: 300;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 6px 12px;
}

.lesson-header { margin-bottom: 40px; }
.lesson-phase {
  font-size: 11px;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 1.2px;
  color: var(--accent);
  margin-bottom: 8px;
}
.lesson-title {
  font-size: 32px;
  font-weight: 700;
  letter-spacing: -0.5px;
  line-height: 1.2;
  margin-bottom: 12px;
}
.lesson-meta {
  display: flex;
  gap: 16px;
  font-size: 13px;
  color: var(--muted);
}
.lesson-meta .tag {
  background: var(--surface2);
  border: 1px solid var(--border);
  border-radius: 20px;
  padding: 3px 10px;
  font-size: 12px;
}
.lesson-meta .tag.gpu { border-color: var(--yellow); color: var(--yellow); }

/* ── Prose ── */
.prose h2 {
  font-size: 22px;
  font-weight: 600;
  margin: 40px 0 14px;
  color: var(--text);
  border-bottom: 1px solid var(--border);
  padding-bottom: 8px;
}
.prose h3 {
  font-size: 16px;
  font-weight: 600;
  margin: 24px 0 10px;
  color: var(--accent2);
}
.prose p { margin-bottom: 14px; color: var(--text); font-size: 15px; }
.prose ul, .prose ol {
  margin: 10px 0 16px 20px;
  font-size: 15px;
}
.prose li { margin-bottom: 6px; }
.prose strong { color: #fff; font-weight: 600; }
.prose em { color: var(--accent2); font-style: italic; }

.prose table {
  width: 100%;
  border-collapse: collapse;
  font-size: 14px;
  margin: 20px 0;
}
.prose th {
  background: var(--surface2);
  border: 1px solid var(--border);
  padding: 10px 14px;
  text-align: left;
  font-weight: 600;
  color: var(--accent);
}
.prose td {
  border: 1px solid var(--border);
  padding: 9px 14px;
}
.prose tr:nth-child(even) td { background: rgba(255,255,255,0.02); }

.prose pre {
  background: #0d1117;
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 18px 20px;
  overflow-x: auto;
  margin: 16px 0 20px;
  font-size: 13.5px;
  line-height: 1.6;
}
.prose code {
  font-family: 'JetBrains Mono', 'Fira Code', monospace;
  color: #e2e8f0;
}
.prose p code, .prose li code {
  background: var(--surface2);
  padding: 2px 6px;
  border-radius: 4px;
  font-size: 13px;
  color: var(--pink);
}

.callout {
  background: rgba(108,142,245,0.08);
  border-left: 3px solid var(--accent);
  border-radius: 0 8px 8px 0;
  padding: 14px 18px;
  margin: 20px 0;
  font-size: 14px;
}
.callout.green { background: rgba(74,222,128,0.07); border-color: var(--green); }
.callout.yellow { background: rgba(251,191,36,0.07); border-color: var(--yellow); }

/* ── Lesson nav ── */
.lesson-nav {
  display: flex;
  justify-content: space-between;
  margin-top: 60px;
  padding-top: 24px;
  border-top: 1px solid var(--border);
}
.nav-btn {
  display: flex;
  flex-direction: column;
  text-decoration: none;
  padding: 14px 20px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 10px;
  max-width: 280px;
  transition: border-color 0.15s;
}
.nav-btn:hover { border-color: var(--accent); }
.nav-btn .dir { font-size: 11px; color: var(--muted); margin-bottom: 4px; text-transform: uppercase; letter-spacing: 0.8px; }
.nav-btn .ttl { font-size: 14px; color: var(--text); font-weight: 500; }
.nav-btn.next { align-items: flex-end; }

/* ── Home ── */
.home-hero {
  padding: 56px 40px 32px;
  max-width: 820px;
  margin: 0 auto;
}
.home-hero h1 {
  font-size: 38px;
  font-weight: 800;
  letter-spacing: -0.8px;
  line-height: 1.15;
  margin-bottom: 16px;
}
.home-hero h1 span { color: var(--accent); }
.home-hero p { font-size: 17px; color: var(--muted); max-width: 560px; }

.phases-grid {
  max-width: 820px;
  margin: 0 auto;
  padding: 0 40px 80px;
  display: flex;
  flex-direction: column;
  gap: 8px;
}

.phase-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 18px 22px;
  text-decoration: none;
  display: flex;
  align-items: center;
  gap: 18px;
  transition: border-color 0.15s, background 0.15s;
}
.phase-card:hover { border-color: var(--accent); background: var(--surface2); }

.phase-num {
  font-size: 22px;
  font-weight: 800;
  color: var(--border);
  width: 36px;
  flex-shrink: 0;
  text-align: center;
}
.phase-card:hover .phase-num { color: var(--accent); }

.phase-info h3 { font-size: 15px; font-weight: 600; color: var(--text); margin-bottom: 3px; }
.phase-info p { font-size: 13px; color: var(--muted); }

.phase-badge {
  margin-left: auto;
  font-size: 11px;
  background: var(--surface2);
  border: 1px solid var(--border);
  border-radius: 20px;
  padding: 3px 10px;
  color: var(--muted);
  white-space: nowrap;
  flex-shrink: 0;
}

/* ── Home page section cards ── */
.section-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 12px;
  overflow: hidden;
  transition: border-color 0.15s;
}
.section-card:hover { border-color: #3e4468; }

.section-header {
  display: flex;
  align-items: center;
  gap: 16px;
  padding: 18px 22px 14px;
  border-bottom: 1px solid var(--border);
}
.phase-badge.gpu { border-color: var(--yellow); color: var(--yellow); }

.section-lessons {
  display: flex;
  flex-wrap: wrap;
  gap: 7px;
  padding: 14px 22px 16px;
}

.topic-pill {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  background: var(--surface2);
  border: 1px solid var(--border);
  border-radius: 20px;
  padding: 4px 12px;
  font-size: 12.5px;
  color: var(--muted);
  text-decoration: none;
  transition: all 0.15s;
}
.topic-pill:hover { border-color: var(--accent); color: var(--text); }
.topic-pill.ready { border-color: rgba(74,222,128,0.35); color: var(--text); }
.topic-pill.ready:hover { border-color: var(--green); }

.dot {
  width: 6px; height: 6px;
  border-radius: 50%;
  background: var(--border);
  flex-shrink: 0;
}
.dot.green { background: var(--green); }

/* ── Generate box ── */
.generate-box {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 18px 22px;
  max-width: 480px;
  margin: 0 auto;
  text-align: left;
}
.copy-prompt {
  display: flex;
  align-items: center;
  justify-content: space-between;
  background: #0d1117;
  border: 1px solid var(--border);
  border-radius: 7px;
  padding: 12px 14px;
  cursor: pointer;
  transition: border-color 0.15s;
  gap: 12px;
}
.copy-prompt:hover { border-color: var(--accent); }
.copy-prompt code { font-family: 'JetBrains Mono', monospace; font-size: 13px; color: var(--accent2); }
.copy-icon { font-size: 15px; flex-shrink: 0; }

/* ── Status dot color ── */
.status-dot.green { background: var(--green); }

/* ── Google sign-in button ── */
.google-btn {
  display: inline-flex;
  align-items: center;
  gap: 7px;
  background: var(--surface2);
  border: 1px solid var(--border);
  color: var(--text);
  font-size: 12px;
  font-weight: 500;
  padding: 7px 12px;
  border-radius: 7px;
  text-decoration: none;
  transition: border-color 0.15s, background 0.15s;
  width: 100%;
  justify-content: center;
  margin-top: 4px;
}
.google-btn:hover { border-color: #4285F4; background: rgba(66,133,244,0.08); }

/* ── Scrollbar ── */
::-webkit-scrollbar { width: 6px; }
::-webkit-scrollbar-track { background: transparent; }
::-webkit-scrollbar-thumb { background: var(--border); border-radius: 3px; }