:root {
  color-scheme: dark;

  --bg: #0b0d12;
  --card: #121723;
  --text: #e9eef7;
  --muted: #b6c0d3;
  --border: rgba(255, 255, 255, 0.12);
  --shadow: rgba(0, 0, 0, 0.45);
  --link: #7aa7ff;

  --radius: 12px;
  --maxw: 900px;
  --gap: 16px;
}

* { box-sizing: border-box; }

body {
  font-family: system-ui, -apple-system, Segoe UI, Roboto, sans-serif;
  margin: 0;
  padding: 24px;
  background: var(--bg);
  color: var(--text);
  line-height: 1.6;
}

header, main {
  max-width: var(--maxw);
  margin: 0 auto;
}

a { color: var(--link); }

nav a {
  margin-right: 12px;
  text-decoration: none;
}

nav a:hover { text-decoration: underline; }

.card {
  background: var(--card);
  padding: 18px;
  border-radius: var(--radius);
  border: 1px solid var(--border);
  box-shadow: 0 2px 10px var(--shadow);
  margin: var(--gap) 0;
}

header.card {
  max-width: var(--maxw);
  margin: var(--gap) auto;
  text-align: center;
}

header.card nav {
  display: flex;
  justify-content: center;
  gap: 14px;
  flex-wrap: wrap;
}

header.card nav a {
  margin-right: 0;
  font-size: 0.95rem;
  padding: 8px 12px;
}

h1, h2 {
  line-height: 1.2;
  margin-top: 0;
}

.youtube-thumb{
  width: 100%;
  height: auto;
  display: block;
  border-radius: 12px;
  margin: 0.5rem 0 0.25rem;
  border: 1px solid var(--border);
}

.youtube-thumb:hover {
  opacity: 0.95;
}

small, .muted { color: var(--muted); }

button {
  padding: 10px 14px;
  border-radius: 10px;
  border: 1px solid var(--border);
  background: transparent;
  color: var(--text);
  cursor: pointer;
}

.gallery {
  display: grid;
  grid-template-columns: 1fr;
  gap: 14px;
}

.diagram-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: 14px;
}

@media (min-width: 700px) {
  .diagram-grid {
    grid-template-columns: 1fr 1fr;
  }
}

.figure img {
  width: 100%;
  max-width: 450px; /* can make smaller */
  height: auto;
  display: block;
  margin: 0 auto;
  border-radius: 12px;
  border: 1px solid var(--border);
}

.figure figcaption {
  margin-top: 8px;
  color: var(--muted);
  font-size: 0.95rem;
  text-align: center;
}

pre {
  background: #0f172a;
  color: #e2e8f0;
  padding: 12px 14px;
  border-radius: 12px;
  overflow-x: auto;
  line-height: 1.35;
  font-size: 0.9rem;
  border: 1px solid rgba(255,255,255,0.08);
}

code {
  font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, "Liberation Mono", "Courier New", monospace;
}

.code-caption {
  margin: 10px 0 6px;
  font-weight: 600;
  opacity: 0.9;
}