:root {
  --ink: #102429;
  --ink-soft: #3a545b;
  --paper: #edf3f4;
  --paper-2: #e2ecee;
  --teal: #0f7a72;
  --teal-deep: #0a5c56;
  --amber: #c45c16;
  --line: rgba(16, 36, 41, 0.12);
  --shadow: 0 18px 50px rgba(16, 36, 41, 0.08);
  --radius: 14px;
  --font-display: "Syne", sans-serif;
  --font-body: "IBM Plex Sans", sans-serif;
  --font-mono: "IBM Plex Mono", monospace;
  --max: 920px;
  --catalog-w: 300px;
}

*,
*::before,
*::after {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  color: var(--ink);
  font-family: var(--font-body);
  font-size: 17px;
  line-height: 1.7;
  background:
    radial-gradient(1200px 600px at 10% -10%, rgba(15, 122, 114, 0.18), transparent 55%),
    radial-gradient(900px 500px at 95% 5%, rgba(196, 92, 22, 0.12), transparent 50%),
    linear-gradient(165deg, #f4f8f8 0%, var(--paper) 45%, var(--paper-2) 100%);
  min-height: 100vh;
}

.noise {
  pointer-events: none;
  position: fixed;
  inset: 0;
  opacity: 0.04;
  background-image: url("data:image/svg+xml,%3Csvg viewBox='0 0 200 200' xmlns='http://www.w3.org/2000/svg'%3E%3Cfilter id='n'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='0.85' numOctaves='4' stitchTiles='stitch'/%3E%3C/filter%3E%3Crect width='100%25' height='100%25' filter='url(%23n)'/%3E%3C/svg%3E");
  z-index: 0;
}

.layout {
  position: relative;
  z-index: 1;
  display: grid;
  grid-template-columns: var(--catalog-w) minmax(0, 1fr);
  min-height: 100vh;
  align-items: start;
}

/* 左侧：问题目录 */
.catalog {
  position: sticky;
  top: 0;
  z-index: 20;
  width: var(--catalog-w);
  height: 100vh;
  border-right: 1px solid var(--line);
  background: rgba(244, 249, 249, 0.97);
  backdrop-filter: blur(12px);
}

.catalog__panel {
  display: flex;
  flex-direction: column;
  height: 100%;
  padding: 1.1rem 0.85rem 1rem;
  gap: 0.75rem;
}

.catalog__head {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 0.5rem;
  padding: 0 0.35rem;
}

.catalog__label {
  margin: 0;
  font-family: var(--font-display);
  font-size: 0.82rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--teal-deep);
}

.catalog-close {
  display: none;
  width: 2rem;
  height: 2rem;
  border: none;
  border-radius: 8px;
  background: transparent;
  color: var(--ink-soft);
  font-size: 1.4rem;
  line-height: 1;
  cursor: pointer;
}

.catalog-toggle {
  display: none;
  align-items: center;
  justify-content: center;
  padding: 0.45rem 0.85rem;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: rgba(255, 255, 255, 0.65);
  color: var(--ink);
  font-family: var(--font-body);
  font-size: 0.9rem;
  font-weight: 600;
  cursor: pointer;
}

.catalog-toggle:hover {
  border-color: var(--teal);
  color: var(--teal-deep);
}

.tree {
  flex: 1;
  overflow-y: auto;
  padding: 0.15rem 0.2rem 0.5rem;
  display: flex;
  flex-direction: column;
  gap: 0.2rem;
}

.tree__leaf,
.tree__q {
  display: block;
  text-decoration: none;
  color: inherit;
  border-radius: 8px;
  transition: background 0.15s ease, color 0.15s ease;
}

.tree__leaf {
  padding: 0.42rem 0.55rem;
  font-size: 0.84rem;
  color: var(--ink-soft);
  line-height: 1.35;
}

.tree__leaf--root {
  font-weight: 600;
  color: var(--ink);
  margin-bottom: 0.25rem;
}

.tree__leaf:hover,
.tree__q:hover {
  background: rgba(15, 122, 114, 0.08);
  color: var(--teal-deep);
}

.tree__leaf.is-active,
.tree__q.is-active {
  background: rgba(15, 122, 114, 0.14);
  color: var(--teal-deep);
  font-weight: 600;
}

.tree__branch {
  border-radius: 10px;
}

.tree__branch.is-current {
  background: rgba(15, 122, 114, 0.05);
}

.tree__summary {
  list-style: none;
  display: flex;
  align-items: flex-start;
  gap: 0.15rem;
  cursor: pointer;
  padding: 0.15rem;
  border-radius: 8px;
}

.tree__summary::-webkit-details-marker {
  display: none;
}

.tree__summary::before {
  content: "▸";
  flex: 0 0 auto;
  width: 1rem;
  margin-top: 0.55rem;
  font-size: 0.7rem;
  color: var(--teal);
  transition: transform 0.15s ease;
}

.tree__branch[open] > .tree__summary::before {
  transform: rotate(90deg);
}

.tree__q {
  flex: 1;
  display: grid;
  gap: 0.1rem;
  padding: 0.45rem 0.4rem;
  min-width: 0;
}

.tree__id {
  font-family: var(--font-mono);
  font-size: 0.72rem;
  font-weight: 500;
  color: var(--teal);
}

.tree__text {
  font-size: 0.88rem;
  font-weight: 650;
  line-height: 1.35;
}

.tree__kids {
  display: flex;
  flex-direction: column;
  gap: 0.08rem;
  margin: 0.1rem 0 0.35rem 1.05rem;
  padding-left: 0.55rem;
  border-left: 1px solid rgba(15, 122, 114, 0.22);
}

.catalog__switcher {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 0.45rem;
  padding-top: 0.35rem;
  border-top: 1px solid var(--line);
}

.catalog__btn {
  padding: 0.55rem 0.4rem;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: rgba(255, 255, 255, 0.7);
  color: var(--ink);
  font-family: var(--font-body);
  font-size: 0.82rem;
  font-weight: 600;
  cursor: pointer;
}

.catalog__btn:hover:not(:disabled) {
  border-color: var(--teal);
  color: var(--teal-deep);
}

.catalog__btn:disabled {
  opacity: 0.4;
  cursor: not-allowed;
}

.catalog-backdrop {
  display: none;
}

/* 右侧：完整文档 */
.doc {
  min-width: 0;
  position: relative;
  z-index: 1;
}

.topbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  padding: 1rem 1.75rem 0.5rem;
  position: sticky;
  top: 0;
  z-index: 10;
  background: linear-gradient(180deg, rgba(244, 248, 248, 0.96), rgba(244, 248, 248, 0.82));
  backdrop-filter: blur(8px);
}

.brand {
  font-family: var(--font-display);
  font-weight: 800;
  font-size: 1.15rem;
  letter-spacing: -0.03em;
  color: var(--ink);
  text-decoration: none;
}

main {
  padding: 0 1.75rem 2rem;
}

.footer {
  padding: 0 1.75rem 2.5rem;
  color: var(--ink-soft);
  font-size: 0.9rem;
}

.footer a {
  color: var(--teal-deep);
}

.hero,
.toc,
.question {
  max-width: var(--max);
}

.q-switch {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  margin-top: 2rem;
  padding-top: 1.25rem;
  border-top: 1px solid var(--line);
}

.q-switch a {
  color: var(--teal-deep);
  text-decoration: none;
  font-weight: 600;
  font-size: 0.92rem;
}

.q-switch a:hover {
  text-decoration: underline;
}

.q-switch__spacer {
  flex: 1;
}

.verdict,
.block,
.question,
#top {
  scroll-margin-top: 4rem;
}

.hero {
  display: grid;
  grid-template-columns: 1.15fr 0.85fr;
  gap: 2rem;
  align-items: center;
  max-width: var(--max);
  margin: 0;
  padding: 2.5rem 0 3.5rem;
  min-height: calc(100vh - 72px);
}

.hero__brand {
  margin: 0 0 0.75rem;
  font-family: var(--font-display);
  font-weight: 800;
  font-size: clamp(2.4rem, 5vw, 3.6rem);
  letter-spacing: -0.04em;
  line-height: 1;
  color: var(--teal-deep);
  animation: rise 0.8s ease both;
}

.hero h1 {
  margin: 0 0 1rem;
  font-family: var(--font-display);
  font-weight: 700;
  font-size: clamp(1.55rem, 3.2vw, 2.15rem);
  letter-spacing: -0.03em;
  line-height: 1.25;
  max-width: 16ch;
  animation: rise 0.8s ease 0.08s both;
}

.hero__lead {
  margin: 0 0 1.75rem;
  max-width: 36ch;
  color: var(--ink-soft);
  animation: rise 0.8s ease 0.16s both;
}

.hero__cta {
  display: flex;
  flex-wrap: wrap;
  gap: 0.75rem;
  animation: rise 0.8s ease 0.24s both;
}

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: 0.75rem 1.2rem;
  border-radius: 10px;
  font-weight: 600;
  font-size: 0.95rem;
  text-decoration: none;
  transition: transform 0.2s ease, background 0.2s ease, color 0.2s ease;
}

.btn:hover {
  transform: translateY(-1px);
}

.btn--primary {
  background: var(--teal);
  color: #f7fffe;
}

.btn--primary:hover {
  background: var(--teal-deep);
}

.btn--ghost {
  background: transparent;
  color: var(--ink);
  border: 1px solid var(--line);
}

.btn--ghost:hover {
  border-color: var(--teal);
  color: var(--teal-deep);
}

.hero__visual {
  display: grid;
  place-items: center;
  min-height: 320px;
}

.orbit {
  position: relative;
  width: min(340px, 80vw);
  aspect-ratio: 1;
  animation: float 6s ease-in-out infinite;
}

.orbit__ring {
  position: absolute;
  inset: 12%;
  border: 1.5px dashed rgba(15, 122, 114, 0.35);
  border-radius: 50%;
  animation: spin 18s linear infinite;
}

.orbit__core {
  position: absolute;
  inset: 34%;
  display: grid;
  place-items: center;
  border-radius: 50%;
  background: linear-gradient(145deg, #147f77, #0d5f59);
  color: #e8fffc;
  font-family: var(--font-display);
  font-weight: 700;
  letter-spacing: 0.04em;
  box-shadow: var(--shadow);
}

.orbit__node {
  position: absolute;
  padding: 0.45rem 0.7rem;
  border-radius: 999px;
  background: rgba(255, 255, 255, 0.72);
  backdrop-filter: blur(8px);
  border: 1px solid var(--line);
  font-family: var(--font-mono);
  font-size: 0.78rem;
  font-weight: 500;
  color: var(--ink);
}

.orbit__node--a { top: 6%; left: 38%; }
.orbit__node--b { right: 2%; top: 46%; }
.orbit__node--c { bottom: 8%; left: 28%; }

.toc,
.question {
  max-width: var(--max);
  margin-right: auto;
  margin-left: 0;
  padding: 0 0 3.5rem;
}

.section-label {
  margin: 0 0 1rem;
  font-family: var(--font-display);
  font-size: 0.95rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--teal-deep);
}

.toc__list {
  display: grid;
  gap: 0.75rem;
}

.toc__item {
  display: grid;
  grid-template-columns: auto 1fr auto;
  gap: 0.75rem 1rem;
  align-items: baseline;
  padding: 1rem 1.15rem;
  text-decoration: none;
  color: inherit;
  border-bottom: 1px solid var(--line);
  transition: background 0.2s ease, padding-left 0.2s ease;
}

.toc__item:hover {
  background: rgba(15, 122, 114, 0.06);
  padding-left: 1.35rem;
}

.toc__id {
  font-family: var(--font-mono);
  font-weight: 500;
  color: var(--teal);
}

.toc__title {
  font-weight: 600;
}

.toc__meta {
  font-size: 0.85rem;
  color: var(--ink-soft);
}

.question {
  padding-top: 1rem;
  scroll-margin-top: 5rem;
}

.question + .question {
  border-top: 1px solid var(--line);
  padding-top: 3rem;
}

.question__id {
  margin: 0 0 0.5rem;
  font-family: var(--font-mono);
  font-size: 0.85rem;
  color: var(--amber);
  letter-spacing: 0.04em;
}

.question__head h2 {
  margin: 0 0 1rem;
  font-family: var(--font-display);
  font-size: clamp(1.35rem, 2.5vw, 1.75rem);
  letter-spacing: -0.02em;
  line-height: 1.35;
}

.tags {
  display: flex;
  flex-wrap: wrap;
  gap: 0.45rem;
  margin: 0;
  padding: 0;
  list-style: none;
}

.tags li {
  font-size: 0.8rem;
  color: var(--ink-soft);
  border: 1px solid var(--line);
  padding: 0.2rem 0.55rem;
  border-radius: 6px;
}

.verdict {
  margin: 1.75rem 0;
  padding: 1.25rem 1.35rem;
  border-left: 3px solid var(--teal);
  background: linear-gradient(90deg, rgba(15, 122, 114, 0.08), transparent 80%);
}

.verdict h3,
.block h3 {
  margin: 0 0 0.75rem;
  font-family: var(--font-display);
  font-size: 1.05rem;
  letter-spacing: -0.01em;
}

.verdict p {
  margin: 0;
}

.block {
  margin: 2rem 0;
}

.block h4 {
  margin: 0 0 0.4rem;
  font-family: var(--font-display);
  font-size: 1rem;
}

blockquote {
  margin: 0 0 1rem;
  padding: 1rem 1.15rem;
  background: rgba(255, 255, 255, 0.45);
  border-radius: var(--radius);
  border: 1px solid var(--line);
}

.punch {
  font-weight: 600;
  color: var(--teal-deep);
}

.table-wrap {
  overflow-x: auto;
  margin: 1rem 0;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: rgba(255, 255, 255, 0.4);
}

table {
  width: 100%;
  border-collapse: collapse;
  font-size: 0.92rem;
}

th,
td {
  padding: 0.7rem 0.85rem;
  text-align: left;
  border-bottom: 1px solid var(--line);
  vertical-align: top;
}

th {
  font-weight: 600;
  background: rgba(15, 122, 114, 0.06);
}

tr:last-child td {
  border-bottom: none;
}

.pipeline {
  margin: 0 0 1rem;
  padding-left: 1.2rem;
}

.pipeline li {
  margin: 0.45rem 0;
}

.bullets {
  margin: 0;
  padding-left: 1.2rem;
}

.bullets li {
  margin: 0.4rem 0;
}

.code {
  margin: 1rem 0;
  padding: 1rem 1.1rem;
  overflow-x: auto;
  border-radius: var(--radius);
  background: #123038;
  color: #d7ece8;
  font-family: var(--font-mono);
  font-size: 0.84rem;
  line-height: 1.55;
}

.code code {
  font-family: inherit;
}

.loop {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 0.5rem;
  margin: 0 0 1rem;
}

.loop__step {
  padding: 0.55rem 0.9rem;
  border-radius: 10px;
  background: rgba(15, 122, 114, 0.1);
  border: 1px solid rgba(15, 122, 114, 0.2);
  font-family: var(--font-mono);
  font-size: 0.85rem;
  font-weight: 500;
}

.loop__arrow {
  color: var(--teal);
  font-weight: 600;
}

.methods {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 0.85rem;
}

.method {
  padding: 1rem 1.05rem;
  border-top: 2px solid var(--teal);
  background: rgba(255, 255, 255, 0.35);
}

.method p {
  margin: 0;
  font-size: 0.92rem;
  color: var(--ink-soft);
}

.followups details {
  margin: 0.55rem 0;
  padding: 0.75rem 0.9rem;
  border: 1px solid var(--line);
  border-radius: 10px;
  background: rgba(255, 255, 255, 0.35);
}

.followups summary {
  cursor: pointer;
  font-weight: 600;
  list-style: none;
}

.followups summary::-webkit-details-marker {
  display: none;
}

.followups summary::before {
  content: "+";
  display: inline-block;
  width: 1.1rem;
  color: var(--teal);
  font-family: var(--font-mono);
}

.followups details[open] summary::before {
  content: "–";
}

.followups details p {
  margin: 0.65rem 0 0;
  color: var(--ink-soft);
}

.reveal {
  opacity: 0;
  transform: translateY(18px);
  transition: opacity 0.55s ease, transform 0.55s ease;
}

.reveal.is-visible {
  opacity: 1;
  transform: none;
}

@keyframes rise {
  from {
    opacity: 0;
    transform: translateY(16px);
  }
  to {
    opacity: 1;
    transform: none;
  }
}

@keyframes float {
  0%, 100% { transform: translateY(0); }
  50% { transform: translateY(-10px); }
}

@keyframes spin {
  to { transform: rotate(360deg); }
}

@media (max-width: 980px) {
  .layout {
    grid-template-columns: 1fr;
  }

  .catalog-toggle {
    display: inline-flex;
  }

  .catalog {
    position: fixed;
    top: 0;
    left: 0;
    width: min(320px, 88vw);
    height: 100vh;
    transform: translateX(-105%);
    transition: transform 0.25s ease;
    box-shadow: var(--shadow);
    z-index: 50;
  }

  .catalog.is-open {
    transform: translateX(0);
  }

  .catalog-close {
    display: inline-flex;
    align-items: center;
    justify-content: center;
  }

  .catalog-backdrop {
    position: fixed;
    inset: 0;
    z-index: 45;
    display: block;
    background: rgba(16, 36, 41, 0.35);
    opacity: 0;
    pointer-events: none;
    transition: opacity 0.25s ease;
  }

  .catalog-backdrop.is-open {
    opacity: 1;
    pointer-events: auto;
  }

  .toc,
  .question,
  .hero {
    margin-left: auto;
    margin-right: auto;
  }
}

@media (max-width: 860px) {
  .hero {
    grid-template-columns: 1fr;
    min-height: auto;
    padding-top: 1.5rem;
  }

  .hero h1 {
    max-width: none;
  }

  .hero__visual {
    min-height: 240px;
  }

  .toc__item {
    grid-template-columns: auto 1fr;
  }

  .toc__meta {
    grid-column: 2;
  }

  .methods {
    grid-template-columns: 1fr;
  }
}

@media (max-width: 560px) {
  body {
    font-size: 16px;
  }

  .q-switch {
    flex-direction: column;
  }
}

@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  .hero__brand,
  .hero h1,
  .hero__lead,
  .hero__cta,
  .orbit,
  .orbit__ring,
  .reveal,
  .catalog,
  .catalog-backdrop {
    animation: none !important;
    transition: none !important;
    opacity: 1;
    transform: none;
  }
}

.tree__chapter {
  margin: 0.85rem 0 0.25rem;
  padding: 0 0.35rem;
  font-family: var(--font-display);
  font-size: 0.72rem;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  color: var(--amber);
}

.answer-body > h2 {
  margin-top: 1.75rem;
  font-family: var(--font-display);
  font-size: 1.15rem;
}

.answer-body > h3 {
  margin-top: 1.25rem;
  font-family: var(--font-display);
  font-size: 1.02rem;
}

.answer-body table {
  width: 100%;
  border-collapse: collapse;
  font-size: 0.92rem;
  margin: 1rem 0;
}

.answer-body th,
.answer-body td {
  border: 1px solid var(--line);
  padding: 0.55rem 0.7rem;
  text-align: left;
  vertical-align: top;
}

.answer-body th {
  background: rgba(15, 122, 114, 0.06);
}

.answer-body pre {
  margin: 1rem 0;
  padding: 1rem 1.1rem;
  overflow-x: auto;
  border-radius: var(--radius);
  background: #123038;
  color: #d7ece8;
  font-family: var(--font-mono);
  font-size: 0.84rem;
}

.answer-body blockquote {
  margin: 0 0 1rem;
  padding: 1rem 1.15rem;
  background: rgba(255, 255, 255, 0.45);
  border-radius: var(--radius);
  border: 1px solid var(--line);
}