:root {
  color-scheme: light;
  --ink: #111317;
  --muted: #5f6673;
  --line: #d8dde5;
  --soft: #f4f7fb;
  --panel: #ffffff;
  --blue: #1f6feb;
  --teal: #0a6b65;
  --gold: #b88215;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: Inter, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  color: var(--ink);
  background: #ffffff;
  line-height: 1.55;
  overflow-x: hidden;
}

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

.wrap {
  width: min(1120px, calc(100% - 32px));
  margin: 0 auto;
}

header {
  position: sticky;
  top: 0;
  z-index: 20;
  border-bottom: 1px solid var(--line);
  background: rgba(255, 255, 255, 0.96);
  backdrop-filter: blur(12px);
}

.nav {
  display: flex;
  align-items: center;
  justify-content: space-between;
  min-height: 68px;
  gap: 16px;
}

.brand {
  font-weight: 800;
  letter-spacing: 0;
}

.nav-links {
  display: flex;
  gap: 18px;
  flex-wrap: wrap;
  min-width: 0;
  font-size: 0.95rem;
}

.hero {
  padding: 72px 0 48px;
  background: linear-gradient(180deg, #f7fbff 0%, #ffffff 80%);
}

.eyebrow {
  margin: 0 0 12px;
  color: var(--teal);
  font-weight: 800;
  text-transform: uppercase;
  font-size: 0.82rem;
}

h1 {
  margin: 0;
  max-width: 960px;
  font-size: clamp(2.2rem, 5vw, 4.8rem);
  line-height: 1.02;
  letter-spacing: 0;
}

h2 {
  margin: 0 0 18px;
  font-size: clamp(1.6rem, 3vw, 2.3rem);
  letter-spacing: 0;
}

h3 {
  margin: 0 0 8px;
  font-size: 1.08rem;
}

p {
  margin: 0;
}

p + p {
  margin-top: 14px;
}

.lead {
  max-width: 780px;
  margin-top: 22px;
  color: var(--muted);
  font-size: 1.16rem;
}

.actions {
  display: flex;
  gap: 12px;
  flex-wrap: wrap;
  margin-top: 28px;
}

.button {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-height: 44px;
  padding: 0 18px;
  border: 1px solid var(--line);
  border-radius: 8px;
  color: var(--ink);
  text-decoration: none;
  font-weight: 700;
  background: var(--panel);
}

.button.primary {
  color: #ffffff;
  background: var(--ink);
  border-color: var(--ink);
}

section {
  padding: 48px 0;
  border-top: 1px solid var(--line);
}

.grid {
  display: grid;
  gap: 18px;
}

.grid.three {
  grid-template-columns: repeat(3, minmax(0, 1fr));
}

.grid.four {
  grid-template-columns: repeat(4, minmax(0, 1fr));
}

.grid.two {
  grid-template-columns: repeat(2, minmax(0, 1fr));
}

.card {
  min-width: 0;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--panel);
  padding: 20px;
}

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

.media {
  display: block;
  width: 100%;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--soft);
}

.thumbnail {
  aspect-ratio: 16 / 9;
  object-fit: cover;
  margin-bottom: 14px;
}

.media.pad {
  padding: 16px;
}

.tag-list {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin-top: 20px;
}

.tag {
  border: 1px solid var(--line);
  border-radius: 999px;
  padding: 6px 10px;
  background: #ffffff;
  color: var(--muted);
  font-size: 0.92rem;
}

.proof-list {
  margin: 0;
  padding-left: 20px;
  color: var(--muted);
}

.proof-list li + li {
  margin-top: 8px;
}

.diagram-panel {
  overflow: hidden;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--panel);
  padding: 18px;
}

.diagram-panel .mermaid {
  display: flex;
  justify-content: center;
  min-height: 280px;
  overflow-x: auto;
}

.caption {
  margin-top: 10px;
  color: var(--muted);
  font-size: 0.92rem;
}

.chapter-block {
  width: 100%;
  overflow-x: auto;
  margin: 14px 0 0;
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 14px;
  background: var(--soft);
  color: var(--ink);
  font-family: "Cascadia Mono", "SFMono-Regular", Consolas, monospace;
  font-size: 0.88rem;
  line-height: 1.55;
  white-space: pre-wrap;
}

.download-meta {
  display: grid;
  gap: 12px;
  margin: 0;
}

.download-meta div {
  display: grid;
  gap: 4px;
}

.download-meta dt {
  color: var(--muted);
  font-size: 0.86rem;
  font-weight: 800;
  text-transform: uppercase;
}

.download-meta dd {
  margin: 0;
  overflow-wrap: anywhere;
}

code {
  font-family: "Cascadia Mono", "SFMono-Regular", Consolas, monospace;
}

.download-meta code {
  display: block;
  white-space: normal;
  word-break: break-all;
}

.video-grid {
  display: grid;
  grid-template-columns: 1.1fr 0.9fr;
  gap: 18px;
  align-items: start;
}

.ratio {
  position: relative;
  width: 100%;
  aspect-ratio: 16 / 9;
  overflow: hidden;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--soft);
}

.ratio iframe {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  border: 0;
}

.video-poster {
  position: relative;
  display: block;
  overflow: hidden;
  border: 1px solid var(--line);
  border-radius: 8px;
  aspect-ratio: 16 / 9;
  color: #ffffff;
  background: var(--ink);
}

.video-poster img {
  display: block;
  width: 100%;
  height: 100%;
  object-fit: cover;
}

.video-poster span {
  position: absolute;
  left: 18px;
  bottom: 18px;
  display: inline-flex;
  min-height: 44px;
  align-items: center;
  border-radius: 8px;
  padding: 0 16px;
  background: rgba(17, 19, 23, 0.92);
  color: #ffffff;
  font-weight: 800;
}

footer {
  padding: 32px 0 48px;
  border-top: 1px solid var(--line);
  color: var(--muted);
}

@media (max-width: 780px) {
  .nav {
    align-items: flex-start;
    flex-direction: column;
    padding: 18px 0;
  }

  .hero {
    padding-top: 48px;
  }

  .grid.three,
  .grid.four,
  .grid.two,
  .video-grid {
    grid-template-columns: 1fr;
  }

  .actions {
    flex-direction: column;
    align-items: stretch;
  }

  .button {
    width: 100%;
  }
}