:root {
  --bg: #0e1210;
  --bg-rail: #121816;
  --ink: #e6ebe4;
  --muted: #8a958c;
  --line: #2a342e;
  --accent: #c45c3a;
  --accent-soft: rgba(196, 92, 58, 0.14);
  --paper: #161c18;
  --serif: "Noto Serif TC", "Songti TC", serif;
  --sans: "Source Sans 3", "Noto Sans TC", system-ui, sans-serif;
}

* {
  box-sizing: border-box;
}

html,
body {
  margin: 0;
  min-height: 100%;
  background: var(--bg);
  color: var(--ink);
  font-family: var(--sans);
}

body {
  background-image:
    radial-gradient(ellipse 80% 50% at 10% -10%, rgba(196, 92, 58, 0.12), transparent 55%),
    radial-gradient(ellipse 60% 40% at 100% 0%, rgba(70, 110, 90, 0.1), transparent 50%),
    linear-gradient(180deg, #0e1210 0%, #0b0f0d 100%);
}

.sr {
  position: absolute;
  width: 1px;
  height: 1px;
  overflow: hidden;
  clip: rect(0 0 0 0);
}

.shell {
  display: grid;
  grid-template-columns: minmax(260px, 320px) 1fr;
  min-height: 100vh;
}

.rail {
  position: sticky;
  top: 0;
  height: 100vh;
  overflow: auto;
  background: color-mix(in srgb, var(--bg-rail) 92%, black);
  border-right: 1px solid var(--line);
  padding: 1.25rem 1rem 2rem;
  display: flex;
  flex-direction: column;
  gap: 1rem;
}

.brand .eyebrow {
  margin: 0;
  font-size: 0.75rem;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: var(--accent);
}

.brand-title {
  display: block;
  margin: 0.2rem 0 0;
  font-family: var(--serif);
  font-size: 2rem;
  font-weight: 700;
  color: var(--ink);
  text-decoration: none;
}

.brand-sub {
  margin: 0.25rem 0 0;
  color: var(--muted);
  font-size: 0.9rem;
}

.search-wrap input {
  width: 100%;
  border: 1px solid var(--line);
  background: var(--paper);
  color: var(--ink);
  border-radius: 6px;
  padding: 0.55rem 0.7rem;
  font: inherit;
}

.search-wrap input:focus {
  outline: 2px solid color-mix(in srgb, var(--accent) 55%, transparent);
  border-color: var(--accent);
}

.starter,
.toc {
  display: flex;
  flex-direction: column;
  gap: 0.2rem;
}

.starter {
  padding-bottom: 0.75rem;
  border-bottom: 1px solid var(--line);
}

.sec-label {
  margin: 0.85rem 0 0.35rem;
  font-size: 0.72rem;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--muted);
}

.nav-link {
  display: block;
  text-align: left;
  width: 100%;
  border: 0;
  background: transparent;
  color: var(--ink);
  font: inherit;
  font-size: 0.92rem;
  padding: 0.4rem 0.55rem;
  border-radius: 6px;
  cursor: pointer;
  text-decoration: none;
}

.nav-link:hover,
.nav-link.active {
  background: var(--accent-soft);
  color: #f3d2c4;
}

.nav-link .blurb {
  display: block;
  margin-top: 0.15rem;
  font-size: 0.75rem;
  color: var(--muted);
  line-height: 1.35;
}

.rail-foot {
  margin-top: auto;
  display: flex;
  flex-wrap: wrap;
  gap: 0.75rem;
  padding-top: 1rem;
  border-top: 1px solid var(--line);
  font-size: 0.85rem;
}

.rail-foot a {
  color: var(--muted);
  text-decoration: none;
}

.rail-foot a:hover {
  color: var(--accent);
}

.main {
  min-width: 0;
}

.topbar {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  padding: 0.65rem 1rem;
  border-bottom: 1px solid var(--line);
  background: color-mix(in srgb, var(--bg) 80%, transparent);
  backdrop-filter: blur(8px);
  position: sticky;
  top: 0;
  z-index: 2;
  min-height: 0;
}

@media (min-width: 901px) {
  .topbar {
    display: none;
  }
}

.reader {
  max-width: 46rem;
  margin: 0 auto;
  padding: 2rem 1.5rem 4rem;
}

.home .kicker {
  margin: 0;
  color: var(--accent);
  letter-spacing: 0.08em;
  font-size: 0.85rem;
}

.home h1 {
  margin: 0.4rem 0 0.75rem;
  font-family: var(--serif);
  font-size: clamp(2rem, 4vw, 2.75rem);
  font-weight: 700;
  line-height: 1.15;
}

.lede {
  margin: 0 0 1.5rem;
  color: color-mix(in srgb, var(--ink) 88%, var(--muted));
  line-height: 1.7;
  font-size: 1.05rem;
}

.path {
  margin: 0;
  padding: 1rem 1rem 1rem 1.6rem;
  background: var(--paper);
  border: 1px solid var(--line);
  border-radius: 10px;
  line-height: 1.7;
}

.path li + li {
  margin-top: 0.45rem;
}

.hint {
  margin-top: 1.25rem;
  color: var(--muted);
  font-size: 0.9rem;
}

.md {
  font-size: 1.02rem;
  line-height: 1.75;
}

.md h1,
.md h2,
.md h3,
.md h4 {
  font-family: var(--serif);
  line-height: 1.3;
  margin: 1.6rem 0 0.7rem;
}

.md h1 {
  font-size: 1.85rem;
  border-bottom: 1px solid var(--line);
  padding-bottom: 0.5rem;
}

.md h2 {
  font-size: 1.35rem;
}

.md p,
.md li {
  color: color-mix(in srgb, var(--ink) 92%, var(--muted));
}

.md a {
  color: #e08a6a;
}

.md code {
  font-family: ui-monospace, SFMono-Regular, Menlo, monospace;
  font-size: 0.88em;
  background: #1c2420;
  padding: 0.1em 0.35em;
  border-radius: 4px;
}

.md pre {
  overflow: auto;
  background: #101512;
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 0.9rem 1rem;
}

.md pre code {
  background: transparent;
  padding: 0;
}

.md table {
  width: 100%;
  border-collapse: collapse;
  font-size: 0.92rem;
  margin: 1rem 0;
  display: block;
  overflow-x: auto;
}

.md th,
.md td {
  border: 1px solid var(--line);
  padding: 0.45rem 0.6rem;
  text-align: left;
  vertical-align: top;
}

.md th {
  background: #1a221e;
}

.md blockquote {
  margin: 1rem 0;
  padding: 0.2rem 0 0.2rem 0.9rem;
  border-left: 3px solid var(--accent);
  color: var(--muted);
}

.md hr {
  border: 0;
  border-top: 1px solid var(--line);
  margin: 1.75rem 0;
}

.backdrop {
  display: none;
}

@media (max-width: 900px) {
  .shell {
    grid-template-columns: 1fr;
  }

  .rail {
    position: fixed;
    inset: 0 auto 0 0;
    width: min(86vw, 320px);
    z-index: 20;
    transform: translateX(-105%);
    transition: transform 0.2s ease;
  }

  .rail.open {
    transform: translateX(0);
  }

  .menu-btn {
    display: inline-block;
    border: 1px solid var(--line);
    background: var(--paper);
    color: var(--ink);
    border-radius: 6px;
    padding: 0.35rem 0.65rem;
    font: inherit;
    cursor: pointer;
  }

  .backdrop {
    display: block;
    position: fixed;
    inset: 0;
    background: rgba(0, 0, 0, 0.55);
    z-index: 15;
  }

  .backdrop[hidden] {
    display: none;
  }
}