:root {
  --bg: #f6f7f3;
  --paper: #fffefa;
  --ink: #1d2433;
  --muted: #667085;
  --line: #d8ded2;
  --accent: #24795b;
  --accent-strong: #145a44;
  --blue: #315f91;
  --amber: #a76518;
  --code-bg: #101828;
  --code-text: #eef4ff;
  --soft-green: #e8f4ed;
  --soft-blue: #e8f0f8;
  --soft-amber: #fff2dc;
  color-scheme: light;
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  background:
    linear-gradient(180deg, rgba(36, 121, 91, 0.08), rgba(49, 95, 145, 0) 320px),
    var(--bg);
  color: var(--ink);
  font-family: Inter, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  line-height: 1.75;
}

a {
  color: var(--accent-strong);
  text-decoration-thickness: 0.08em;
  text-underline-offset: 0.16em;
}

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

.topbar {
  position: sticky;
  top: 0;
  z-index: 20;
  border-bottom: 1px solid rgba(29, 36, 51, 0.08);
  background: rgba(246, 247, 243, 0.92);
  backdrop-filter: blur(14px);
}

.topbar-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 24px;
  width: min(1180px, calc(100% - 32px));
  margin: 0 auto;
  min-height: 64px;
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  color: var(--ink);
  font-weight: 750;
  text-decoration: none;
}

.brand-mark {
  display: inline-grid;
  width: 28px;
  height: 28px;
  place-items: center;
  border-radius: 7px;
  background: var(--ink);
  color: #fff;
  font-size: 13px;
}

.topnav {
  display: flex;
  align-items: center;
  gap: 18px;
  font-size: 14px;
}

.course-shell {
  display: grid;
  grid-template-columns: 248px minmax(0, 1fr);
  gap: 42px;
  width: min(1180px, calc(100% - 32px));
  margin: 0 auto;
  padding: 34px 0 72px;
}

.course-nav {
  position: sticky;
  top: 88px;
  align-self: start;
  padding: 20px 0;
  color: var(--muted);
  font-size: 14px;
}

.course-nav h2 {
  margin: 0 0 12px;
  color: var(--ink);
  font-size: 15px;
  line-height: 1.3;
}

.course-nav ol,
.course-nav ul {
  display: grid;
  gap: 8px;
  margin: 0;
  padding-left: 20px;
}

.course-nav a {
  color: var(--muted);
  text-decoration: none;
}

.course-nav a.active,
.course-nav a:hover {
  color: var(--accent-strong);
}

.course-content {
  min-width: 0;
  border: 1px solid rgba(29, 36, 51, 0.08);
  border-radius: 8px;
  background: var(--paper);
  box-shadow: 0 18px 50px rgba(29, 36, 51, 0.06);
}

.article {
  width: min(820px, calc(100% - 40px));
  margin: 0 auto;
  padding: 48px 0 56px;
}

.eyebrow {
  margin: 0 0 8px;
  color: var(--accent);
  font-size: 13px;
  font-weight: 700;
  letter-spacing: 0;
  text-transform: uppercase;
}

h1,
h2,
h3,
h4 {
  color: var(--ink);
  line-height: 1.24;
  letter-spacing: 0;
}

h1 {
  margin: 0 0 14px;
  font-size: clamp(34px, 6vw, 56px);
}

h2 {
  margin: 42px 0 14px;
  padding-top: 8px;
  border-top: 1px solid var(--line);
  font-size: 28px;
}

h3 {
  margin: 30px 0 10px;
  font-size: 21px;
}

h4 {
  margin: 22px 0 8px;
  font-size: 17px;
}

p {
  margin: 0 0 16px;
}

.lead {
  color: #394255;
  font-size: 19px;
  line-height: 1.8;
}

.meta-grid,
.chapter-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 14px;
  margin: 28px 0;
}

.meta-item,
.chapter-link {
  min-width: 0;
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 16px;
  background: #fbfaf4;
}

.meta-item strong,
.chapter-link strong {
  display: block;
  margin-bottom: 4px;
  color: var(--ink);
}

.chapter-link {
  color: var(--ink);
  text-decoration: none;
}

.chapter-link:hover {
  border-color: rgba(36, 121, 91, 0.38);
  background: var(--soft-green);
  color: var(--ink);
}

.callout {
  margin: 24px 0;
  border-left: 4px solid var(--accent);
  border-radius: 8px;
  padding: 16px 18px;
  background: var(--soft-green);
}

.callout.blue {
  border-left-color: var(--blue);
  background: var(--soft-blue);
}

.callout.amber {
  border-left-color: var(--amber);
  background: var(--soft-amber);
}

.callout strong {
  color: var(--ink);
}

.diagram-loop {
  display: grid;
  grid-template-columns: repeat(5, minmax(0, 1fr));
  gap: 10px;
  margin: 24px 0;
}

.diagram-step,
.timeline-step {
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 14px;
  background: #fbfaf4;
}

.diagram-step span,
.timeline-step span {
  display: block;
  margin-bottom: 6px;
  color: var(--accent);
  font-size: 12px;
  font-weight: 700;
}

.timeline {
  display: grid;
  gap: 12px;
  margin: 24px 0;
}

table {
  width: 100%;
  margin: 24px 0;
  border-collapse: collapse;
  font-size: 15px;
}

th,
td {
  border: 1px solid var(--line);
  padding: 12px;
  vertical-align: top;
}

th {
  background: #eff4ea;
  text-align: left;
}

code {
  border-radius: 5px;
  padding: 0.14em 0.34em;
  background: rgba(36, 121, 91, 0.11);
  color: #18543f;
  font-family: "SFMono-Regular", Consolas, "Liberation Mono", monospace;
  font-size: 0.92em;
}

pre {
  overflow-x: auto;
  margin: 22px 0;
  border-radius: 8px;
  padding: 18px;
  background: var(--code-bg);
  color: var(--code-text);
  line-height: 1.55;
}

pre code {
  padding: 0;
  background: transparent;
  color: inherit;
  font-size: 14px;
}

.exercise-list {
  display: grid;
  gap: 14px;
  margin: 22px 0;
  padding: 0;
  list-style: none;
}

.exercise-list li {
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 16px;
  background: #fbfaf4;
}

.chapter-pager {
  display: flex;
  justify-content: space-between;
  gap: 16px;
  margin-top: 42px;
  padding-top: 24px;
  border-top: 1px solid var(--line);
}

.chapter-pager a {
  max-width: 48%;
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 12px 14px;
  color: var(--ink);
  text-decoration: none;
}

.chapter-pager a:hover {
  border-color: rgba(49, 95, 145, 0.38);
  background: var(--soft-blue);
}

.small {
  color: var(--muted);
  font-size: 14px;
}

@media (max-width: 860px) {
  .topbar-inner {
    align-items: flex-start;
    flex-direction: column;
    gap: 8px;
    padding: 12px 0;
  }

  .topnav {
    flex-wrap: wrap;
    gap: 12px;
  }

  .course-shell {
    display: block;
    padding-top: 18px;
  }

  .course-nav {
    position: static;
    margin-bottom: 16px;
    border: 1px solid var(--line);
    border-radius: 8px;
    padding: 14px;
    background: rgba(255, 254, 250, 0.86);
  }

  .article {
    width: min(100% - 28px, 820px);
    padding: 30px 0 42px;
  }

  h1 {
    font-size: 34px;
  }

  h2 {
    font-size: 24px;
  }

  .meta-grid,
  .chapter-grid,
  .diagram-loop {
    grid-template-columns: 1fr;
  }

  .chapter-pager {
    flex-direction: column;
  }

  .chapter-pager a {
    max-width: none;
  }
}