:root {
  color-scheme: light;
  --page: #f4f7f4;
  --paper: #ffffff;
  --paper-soft: #eaf2ed;
  --ink: #0a2118;
  --muted: #52665d;
  --faint: #71827a;
  --line: #cad8d0;
  --line-strong: #9eb7aa;
  --moss: #0b5c3f;
  --fern: #168b61;
  --signal: #1dba86;
  --mint: #d9fceb;
  --amber-soft: #fff2cf;
  --amber-ink: #70470b;
  --code: #091813;
  --code-ink: #dff9ed;
  --header: rgb(244 247 244 / 92%);
  --font-display: "Arial Narrow", "PingFang SC", "Microsoft YaHei", sans-serif;
  --font-body: "PingFang SC", "Microsoft YaHei", system-ui, sans-serif;
  --font-mono: "SFMono-Regular", Consolas, "Liberation Mono", monospace;
}

[data-theme="dark"] {
  color-scheme: dark;
  --page: #07120e;
  --paper: #0d1e17;
  --paper-soft: #132b21;
  --ink: #e9f6ef;
  --muted: #a7bbb0;
  --faint: #849a8e;
  --line: #244536;
  --line-strong: #3d6a56;
  --moss: #58d9a9;
  --fern: #64e1b0;
  --signal: #78edc0;
  --mint: #163d2e;
  --amber-soft: #3a2e15;
  --amber-ink: #ffd886;
  --code: #030b08;
  --code-ink: #dff9ed;
  --header: rgb(7 18 14 / 92%);
}

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

html {
  scroll-behavior: smooth;
  -webkit-font-smoothing: antialiased;
}

body {
  margin: 0;
  background: var(--page);
  color: var(--ink);
  font-family: var(--font-body);
  font-size: 16px;
  line-height: 1.78;
}

a {
  color: inherit;
  text-decoration: none;
}

button {
  font: inherit;
}

.skip-link {
  position: fixed;
  z-index: 100;
  top: 12px;
  left: 12px;
  padding: 10px 14px;
  border-radius: 8px;
  background: var(--ink);
  color: var(--paper);
  transform: translateY(-180%);
}

.skip-link:focus {
  transform: translateY(0);
}

.course-header {
  position: sticky;
  z-index: 30;
  top: 0;
  display: flex;
  min-height: 68px;
  align-items: center;
  justify-content: space-between;
  gap: 24px;
  padding: 0 30px;
  border-bottom: 1px solid var(--line);
  background: var(--header);
  backdrop-filter: blur(16px);
}

.course-brand {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  font-weight: 850;
}

.brand-mark {
  position: relative;
  display: block;
  width: 32px;
  height: 22px;
}

.brand-mark span {
  position: absolute;
  top: 3px;
  width: 17px;
  height: 16px;
  border: 3px solid var(--moss);
  border-radius: 999px;
}

.brand-mark span:first-child {
  left: 0;
  border-right-color: transparent;
}

.brand-mark span:last-child {
  right: 0;
  border-left-color: transparent;
}

.header-actions {
  display: flex;
  align-items: center;
  gap: 8px;
}

.header-actions a,
.header-actions button {
  display: inline-flex;
  min-height: 42px;
  align-items: center;
  justify-content: center;
  padding: 0 14px;
  border: 1px solid var(--line);
  border-radius: 999px;
  background: var(--paper);
  color: var(--muted);
  font-size: 13px;
  font-weight: 750;
}

.header-actions button {
  cursor: pointer;
}

.header-actions a:hover,
.header-actions button:hover {
  border-color: var(--moss);
  color: var(--moss);
}

.course-layout {
  display: grid;
  width: min(1260px, 100%);
  grid-template-columns: 272px minmax(0, 1fr);
  gap: 64px;
  align-items: start;
  margin: 0 auto;
  padding: 52px 32px 96px;
}

.course-sidebar {
  position: sticky;
  top: 112px;
}

.sidebar-label,
.panel-kicker,
.lesson-index {
  margin: 0;
  color: var(--moss);
  font: 800 11px/1.5 var(--font-mono);
  letter-spacing: .14em;
  text-transform: uppercase;
}

.course-sidebar h2 {
  margin: 8px 0 6px;
  font: 850 23px/1.2 var(--font-display);
  letter-spacing: -.02em;
}

.course-sidebar > p:not(.sidebar-label) {
  margin: 0 0 22px;
  color: var(--muted);
  font-size: 13px;
}

.course-sidebar nav,
.mobile-course-nav nav {
  display: grid;
  gap: 3px;
}

.course-step {
  display: grid;
  grid-template-columns: 30px minmax(0, 1fr);
  gap: 8px;
  align-items: center;
  min-height: 45px;
  padding: 7px 10px;
  border-left: 2px solid var(--line);
  color: var(--muted);
  font-size: 13px;
}

.course-step span:first-child {
  color: var(--faint);
  font: 700 11px/1 var(--font-mono);
}

.course-step:hover {
  border-left-color: var(--line-strong);
  background: var(--paper-soft);
  color: var(--ink);
}

.course-step[aria-current="page"] {
  border-left-color: var(--signal);
  background: var(--mint);
  color: var(--ink);
  font-weight: 800;
}

.sidebar-source {
  display: grid;
  gap: 4px;
  margin-top: 24px;
  padding-top: 18px;
  border-top: 1px solid var(--line);
  color: var(--faint);
  font-size: 11px;
}

.sidebar-source code {
  color: var(--muted);
  font-family: var(--font-mono);
}

.mobile-course-nav {
  display: none;
}

.lesson-main {
  min-width: 0;
}

.lesson-article {
  max-width: 820px;
}

.lesson-hero {
  padding: 16px 0 44px;
  border-bottom: 1px solid var(--line);
}

.lesson-hero h1 {
  max-width: 720px;
  margin: 12px 0 18px;
  font: 900 clamp(40px, 6vw, 72px)/1.03 var(--font-display);
  letter-spacing: -.045em;
}

.lesson-summary {
  max-width: 700px;
  margin: 0;
  color: var(--muted);
  font-size: 19px;
}

.lesson-meta {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin-top: 24px;
}

.lesson-meta span {
  padding: 5px 11px;
  border: 1px solid var(--line);
  border-radius: 999px;
  background: var(--paper);
  color: var(--muted);
  font-size: 12px;
  font-weight: 750;
}

.outcome-panel,
.completion-panel,
.source-panel {
  margin: 38px 0 52px;
  padding: 26px 28px;
  border: 1px solid var(--line);
  border-left: 5px solid var(--signal);
  border-radius: 12px;
  background: var(--paper);
}

.outcome-panel {
  display: grid;
  grid-template-columns: 210px minmax(0, 1fr);
  gap: 28px;
}

.outcome-panel h2,
.completion-panel h2,
.pitfall-section h2,
.source-panel h2 {
  margin: 4px 0 0;
  font-size: 21px;
  line-height: 1.3;
}

.outcome-panel ul,
.completion-panel ul {
  display: grid;
  gap: 8px;
  margin: 0;
  padding: 0;
  list-style: none;
}

.outcome-panel li,
.completion-panel li {
  position: relative;
  padding-left: 27px;
}

.outcome-panel li::before,
.completion-panel li::before {
  position: absolute;
  top: 2px;
  left: 0;
  color: var(--signal);
  content: "✓";
  font-weight: 900;
}

.lesson-section {
  margin: 58px 0;
}

.section-number {
  display: inline-grid;
  width: 34px;
  height: 34px;
  place-items: center;
  margin-bottom: 12px;
  border: 1px solid var(--line-strong);
  border-radius: 50%;
  color: var(--moss);
  font: 800 12px/1 var(--font-mono);
}

.lesson-section h2 {
  margin: 0 0 18px;
  font: 850 30px/1.25 var(--font-display);
  letter-spacing: -.025em;
}

.lesson-section p {
  margin: 0 0 16px;
  color: var(--muted);
}

.lesson-section ul {
  display: grid;
  gap: 8px;
  margin: 18px 0;
  padding-left: 22px;
  color: var(--muted);
}

.lesson-note {
  margin: 22px 0 0;
  padding: 16px 18px;
  border-left: 4px solid var(--amber-ink);
  background: var(--amber-soft);
  color: var(--amber-ink);
  font-size: 14px;
}

.code-block {
  overflow: hidden;
  margin: 24px 0;
  border: 1px solid var(--line-strong);
  border-radius: 12px;
  background: var(--code);
  box-shadow: 0 20px 44px rgb(0 0 0 / 10%);
}

.code-head {
  display: flex;
  min-height: 44px;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  padding: 0 12px 0 16px;
  border-bottom: 1px solid rgb(255 255 255 / 12%);
  color: #9bc5b2;
  font: 700 11px/1 var(--font-mono);
}

.copy-button {
  min-height: 34px;
  padding: 0 11px;
  border: 1px solid rgb(255 255 255 / 16%);
  border-radius: 7px;
  background: rgb(255 255 255 / 7%);
  color: #dff9ed;
  cursor: pointer;
  font: 700 11px/1 var(--font-body);
}

.copy-button:hover {
  border-color: var(--signal);
}

pre {
  overflow-x: auto;
  margin: 0;
  padding: 22px;
}

code {
  font-family: var(--font-mono);
}

pre code {
  color: var(--code-ink);
  font-size: 13px;
  line-height: 1.65;
}

.completion-panel {
  border-left-color: var(--moss);
}

.completion-panel h2 {
  margin-bottom: 18px;
}

.pitfall-section {
  margin: 52px 0;
}

.pitfall-list {
  display: grid;
  gap: 10px;
  margin-top: 18px;
}

.pitfall-item {
  display: grid;
  grid-template-columns: minmax(160px, .75fr) minmax(0, 1.25fr);
  gap: 20px;
  padding: 18px 20px;
  border: 1px solid var(--line);
  border-radius: 10px;
  background: var(--paper);
}

.pitfall-item strong {
  line-height: 1.45;
}

.pitfall-item p {
  margin: 0;
  color: var(--muted);
  font-size: 14px;
}

.source-panel {
  display: grid;
  gap: 20px;
  border-left-color: var(--line-strong);
}

.source-panel p {
  margin: 8px 0 0;
  color: var(--muted);
  font-size: 14px;
}

.source-links {
  display: grid;
  gap: 8px;
}

.source-link {
  display: flex;
  min-height: 48px;
  align-items: center;
  justify-content: space-between;
  gap: 18px;
  padding: 10px 14px;
  border: 1px solid var(--line);
  border-radius: 9px;
  color: var(--moss);
  font-size: 13px;
  font-weight: 800;
}

.source-link small {
  overflow: hidden;
  color: var(--faint);
  font: 500 10px/1.4 var(--font-mono);
  text-overflow: ellipsis;
  white-space: nowrap;
}

.source-link:hover {
  border-color: var(--moss);
}

.source-commit {
  overflow-wrap: anywhere;
}

.lesson-pager {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 14px;
  margin-top: 60px;
  padding-top: 28px;
  border-top: 1px solid var(--line);
}

.pager-link,
.pager-placeholder {
  min-height: 88px;
  padding: 16px 18px;
  border: 1px solid var(--line);
  border-radius: 12px;
}

.pager-link {
  display: grid;
  align-content: center;
  background: var(--paper);
}

.pager-link.next {
  text-align: right;
}

.pager-link span {
  color: var(--faint);
  font-size: 11px;
}

.pager-link strong {
  margin-top: 3px;
  color: var(--moss);
}

.pager-link:hover {
  border-color: var(--moss);
}

.pager-placeholder {
  border-style: dashed;
  opacity: .45;
}

a:focus-visible,
button:focus-visible,
summary:focus-visible {
  outline: 3px solid var(--signal);
  outline-offset: 3px;
}

@media (max-width: 920px) {
  .course-layout {
    grid-template-columns: 220px minmax(0, 1fr);
    gap: 36px;
  }

  .outcome-panel {
    grid-template-columns: 1fr;
  }
}

@media (max-width: 760px) {
  .course-header {
    min-height: 60px;
    padding: 0 16px;
  }

  .course-brand span:last-child {
    display: none;
  }

  .header-actions a:nth-child(2) {
    display: none;
  }

  .header-actions a,
  .header-actions button {
    min-height: 42px;
    padding: 0 11px;
  }

  .mobile-course-nav {
    display: block;
    margin: 16px 16px 0;
    border: 1px solid var(--line);
    border-radius: 10px;
    background: var(--paper);
  }

  .mobile-course-nav summary {
    min-height: 48px;
    padding: 11px 14px;
    cursor: pointer;
    color: var(--moss);
    font-size: 13px;
    font-weight: 800;
  }

  .mobile-course-nav nav {
    padding: 0 10px 10px;
  }

  .course-sidebar {
    display: none;
  }

  .course-layout {
    display: block;
    padding: 30px 20px 72px;
  }

  .lesson-hero {
    padding-top: 6px;
  }

  .lesson-hero h1 {
    font-size: clamp(39px, 13vw, 58px);
  }

  .lesson-summary {
    font-size: 17px;
  }

  .outcome-panel,
  .completion-panel,
  .source-panel {
    padding: 22px 20px;
  }

  .lesson-section {
    margin: 48px 0;
  }

  .lesson-section h2 {
    font-size: 26px;
  }

  pre {
    padding: 18px;
  }

  pre code {
    font-size: 12px;
  }

  .pitfall-item {
    grid-template-columns: 1fr;
    gap: 7px;
  }

  .source-link {
    display: grid;
  }

  .source-link small {
    white-space: normal;
  }
}

@media (max-width: 480px) {
  .lesson-pager {
    grid-template-columns: 1fr;
  }

  .pager-link.next {
    text-align: left;
  }
}

@media (prefers-reduced-motion: reduce) {
  html {
    scroll-behavior: auto;
  }
}