:root {
  --sidebar-w: 280px;
  --color-bg: #ffffff;
  --color-fg: #1f1f1f;
  --color-muted: #666;
  --color-primary: #4285f4;
  --color-primary-hover: #3367d6;
  --color-success: #34a853;
  --color-warn: #fbbc04;
  --color-code-bg: #f5f5f5;
  --color-border: #e0e0e0;
  --radius: 8px;
  --font-mono: 'SF Mono', Consolas, Menlo, monospace;
}

@media (prefers-color-scheme: dark) {
  :root {
    --color-bg: #202124;
    --color-fg: #e8eaed;
    --color-muted: #9aa0a6;
    --color-code-bg: #2d2e30;
    --color-border: #3c4043;
  }
}

* { box-sizing: border-box; }

body {
  margin: 0;
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Hiragino Kaku Gothic ProN', 'Yu Gothic', sans-serif;
  background: var(--color-bg);
  color: var(--color-fg);
  line-height: 1.7;
}

.layout {
  display: grid;
  grid-template-columns: var(--sidebar-w) 1fr;
  min-height: 100vh;
}

.sidebar {
  position: sticky;
  top: 0;
  height: 100vh;
  overflow-y: auto;
  padding: 1.5rem 1rem;
  border-right: 1px solid var(--color-border);
  background: color-mix(in srgb, var(--color-fg) 3%, transparent);
}

.logo { margin: 0 0 0.25rem 0; font-size: 1.4rem; }
.tagline { margin: 0 0 1.5rem 0; font-size: 0.85rem; color: var(--color-muted); }

.sidebar nav ol { list-style: none; padding: 0; margin: 0; }
.sidebar nav ol li {
  padding: 0.5rem 0.75rem;
  border-radius: 6px;
  margin-bottom: 0.25rem;
  cursor: pointer;
  color: var(--color-muted);
  font-size: 0.9rem;
  transition: background 0.15s, color 0.15s;
}
.sidebar nav ol li:hover { color: var(--color-fg); background: color-mix(in srgb, var(--color-fg) 5%, transparent); }
.sidebar nav ol li.active {
  background: color-mix(in srgb, var(--color-primary) 12%, transparent);
  color: var(--color-primary);
  font-weight: 600;
}
.sidebar nav ol li.completed::before { content: '✅ '; }

.content {
  padding: 2rem 3rem;
  max-width: 900px;
  min-width: 0;
}

article {
  padding: 2rem 0 3rem;
  border-bottom: 1px solid var(--color-border);
}
article:last-child { border-bottom: none; }

article h1 { margin-top: 0; font-size: 2rem; }
article h2 { margin-top: 2.5rem; font-size: 1.4rem; }
article h3 { margin-top: 1.5rem; font-size: 1.15rem; }

article pre {
  background: var(--color-code-bg);
  padding: 1rem;
  border-radius: 6px;
  overflow-x: auto;
  font-family: var(--font-mono);
  font-size: 0.9rem;
}

article code:not(pre code) {
  background: var(--color-code-bg);
  padding: 0.15rem 0.4rem;
  border-radius: 4px;
  font-size: 0.9em;
  font-family: var(--font-mono);
}

article ul, article ol { padding-left: 1.5rem; }
article li { margin: 0.25rem 0; }

article a {
  color: var(--color-primary);
  text-decoration: none;
}
article a:hover { text-decoration: underline; }

.meta-card {
  background: color-mix(in srgb, var(--color-primary) 8%, transparent);
  border-left: 4px solid var(--color-primary);
  padding: 1rem 1.25rem;
  border-radius: 0 6px 6px 0;
  margin: 1.5rem 0;
  font-size: 0.95rem;
}

.step {
  background: color-mix(in srgb, var(--color-fg) 3%, transparent);
  border-radius: 8px;
  padding: 1.25rem 1.5rem;
  margin: 1.5rem 0;
}
.step h3 { margin-top: 0; }

.checkpoint {
  border: 2px dashed var(--color-primary);
  padding: 1rem 1.25rem;
  border-radius: 8px;
  margin: 2rem 0;
  background: color-mix(in srgb, var(--color-primary) 3%, transparent);
}

.callout {
  background: color-mix(in srgb, var(--color-warn) 12%, transparent);
  border-left: 4px solid var(--color-warn);
  padding: 0.75rem 1rem;
  border-radius: 0 6px 6px 0;
  margin: 1rem 0;
  font-size: 0.95rem;
}

.complete-btn {
  float: right;
  background: transparent;
  border: 1px solid var(--color-border);
  border-radius: 6px;
  padding: 0.4rem 0.8rem;
  cursor: pointer;
  font-size: 0.85rem;
  color: var(--color-muted);
  transition: all 0.15s;
}
.complete-btn:hover { background: color-mix(in srgb, var(--color-primary) 10%, transparent); color: var(--color-primary); }
.complete-btn.completed { color: var(--color-success); border-color: var(--color-success); }

.copy-btn {
  position: absolute;
  top: 0.5rem;
  right: 0.5rem;
  background: color-mix(in srgb, var(--color-fg) 8%, transparent);
  border: 1px solid var(--color-border);
  border-radius: 4px;
  padding: 0.25rem 0.5rem;
  cursor: pointer;
  font-size: 0.75rem;
  color: var(--color-muted);
  opacity: 0;
  transition: opacity 0.15s;
}
pre { position: relative; }
pre:hover .copy-btn { opacity: 1; }
.copy-btn.copied { color: var(--color-success); }

@media (max-width: 768px) {
  .layout { grid-template-columns: 1fr; }
  .sidebar {
    position: static;
    height: auto;
    border-right: none;
    border-bottom: 1px solid var(--color-border);
  }
  .content { padding: 1.5rem; }
}