:root {
  color-scheme: light;
  --canvas: #f1f4f3;
  --paper: #fcfdfc;
  --surface: #f3f6f5;
  --surface-strong: #e8eeeb;
  --ink: #16201d;
  --ink-soft: #4e5d57;
  --muted: #7b8883;
  --line: #dce3e0;
  --accent: #5f8275;
  --accent-strong: #31584a;
  --accent-soft: #e6eeeb;
  --shadow: 0 14px 44px rgba(35, 57, 49, 0.08);
  --body-size: 1rem;
  --reading-width: 72rem;
  --text-width: 54rem;
  --header-height: 4.8rem;
  font-family: "Noto Sans SC", "Source Han Sans SC", "Microsoft YaHei", system-ui, sans-serif;
}

* { box-sizing: border-box; }

html {
  scroll-behavior: smooth;
  scroll-padding-top: calc(var(--header-height) + 1.5rem);
  background: var(--canvas);
}

body {
  margin: 0;
  background: var(--canvas);
  color: var(--ink);
  line-height: 1.7;
  text-rendering: optimizeLegibility;
}

button, select { font: inherit; }
a { color: inherit; }

.skip-link {
  position: fixed;
  top: 0.5rem;
  left: 0.5rem;
  z-index: 30;
  transform: translateY(-160%);
  padding: 0.6rem 0.9rem;
  border-radius: 0.5rem;
  background: var(--accent-strong);
  color: #f7fbf9;
}

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

.site-header {
  position: sticky;
  top: 0;
  z-index: 20;
  height: var(--header-height);
  border-bottom: 1px solid color-mix(in srgb, var(--line) 82%, transparent);
  background: color-mix(in srgb, var(--paper) 94%, transparent);
  backdrop-filter: blur(18px);
}

.header-inner {
  display: grid;
  grid-template-columns: minmax(17rem, 1fr) minmax(28rem, 34rem);
  align-items: center;
  gap: 3rem;
  max-width: 100rem;
  height: 100%;
  margin: 0 auto;
  padding: 0 2rem;
}

.brand { width: fit-content; text-decoration: none; }
.brand-copy { display: grid; line-height: 1.3; }
.brand-copy strong { font-size: 1.05rem; letter-spacing: 0.01em; }
.brand-copy span { margin-top: 0.18rem; color: var(--muted); font-size: 0.72rem; }

.course-progress {
  display: grid;
  grid-template-columns: auto minmax(10rem, 1fr) auto;
  align-items: center;
  gap: 0.85rem;
}

.progress-copy { display: flex; align-items: baseline; gap: 0.4rem; color: var(--ink-soft); font-size: 0.76rem; white-space: nowrap; }
.progress-copy strong { color: var(--ink); font-size: 0.88rem; }
.progress-track { overflow: hidden; height: 0.48rem; border-radius: 999px; background: var(--surface-strong); }
.progress-track span { display: block; width: 0; height: 100%; border-radius: inherit; background: var(--accent); transition: width 220ms ease; }
.progress-count { color: var(--muted); font-size: 0.72rem; font-variant-numeric: tabular-nums; white-space: nowrap; }
.menu-button { display: none; }

.reader-shell {
  display: grid;
  grid-template-columns: 19rem minmax(0, 1fr);
  max-width: 100rem;
  min-height: calc(100dvh - var(--header-height));
  margin: 0 auto;
}

.course-nav { min-width: 0; border-right: 1px solid var(--line); background: var(--canvas); }
.nav-scroll { position: sticky; top: var(--header-height); overflow-y: auto; max-height: calc(100dvh - var(--header-height)); padding: 1.5rem 0.8rem 4rem; scrollbar-width: thin; }
.course-label { margin: 0 0 0.7rem; padding: 0 0.55rem; color: var(--muted); font-size: 0.78rem; font-weight: 700; letter-spacing: 0.05em; }

.current-module { overflow: hidden; border: 1px solid var(--line); border-radius: 0.8rem; background: var(--paper); box-shadow: var(--shadow); }
.module-link { display: grid; grid-template-areas: "number count state" "title title title"; grid-template-columns: minmax(0, 1fr) auto auto; gap: 0.38rem 0.7rem; align-items: center; width: 100%; min-height: 3.25rem; padding: 0.9rem; border: 0; background: var(--accent-soft); color: var(--ink); font: inherit; text-align: left; cursor: pointer; }
.module-link:active { transform: translateY(1px); }
.module-link #current-module-number { grid-area: number; color: var(--accent-strong); font-size: 0.78rem; font-weight: 800; }
.module-link strong { grid-area: title; font-size: 0.9rem; line-height: 1.42; }
.module-link em { grid-area: count; color: var(--muted); font-size: 0.74rem; font-style: normal; white-space: nowrap; }
.module-toggle-state { grid-area: state; min-width: 2rem; color: var(--accent-strong); font-size: 0.72rem; font-weight: 700; text-align: right; white-space: nowrap; }

.section-nav[hidden] { display: none; }
.section-nav ol { display: grid; gap: 0.1rem; margin: 0; padding: 0.5rem 0.45rem 0.65rem; list-style: none; }
.section-nav a { display: block; min-height: 2.65rem; padding: 0.66rem 0.72rem; border-radius: 0.45rem; color: var(--ink-soft); font-size: 0.84rem; line-height: 1.45; text-decoration: none; }
.section-nav a:hover,
.section-nav a.active { background: var(--surface); color: var(--accent-strong); }

.module-overview { margin: 0.8rem 0 0; padding: 0; list-style: none; }
.module-overview li { border-bottom: 1px solid var(--line); }
.module-overview a { display: grid; grid-template-columns: 1.9rem minmax(0, 1fr) auto; gap: 0.5rem; align-items: center; min-height: 3rem; padding: 0.86rem 0.58rem; border-radius: 0.45rem; text-decoration: none; }
.module-overview a:hover,
.module-overview a.active { background: var(--accent-soft); }
.module-overview span { color: var(--accent-strong); font-size: 0.78rem; font-variant-numeric: tabular-nums; }
.module-overview strong { color: var(--ink-soft); font-size: 0.84rem; font-weight: 600; line-height: 1.45; }
.module-overview em { color: var(--muted); font-size: 0.72rem; font-style: normal; white-space: nowrap; }

.reading-stage { width: 100%; min-width: 0; padding: 2rem clamp(2rem, 4vw, 5rem) 5rem; background: var(--paper); }
.lesson-intro { display: flex; align-items: end; justify-content: space-between; gap: 2rem; max-width: var(--reading-width); margin: 0 auto 1.5rem; padding-bottom: 1rem; border-bottom: 1px solid var(--line); }
.module-kicker { margin: 0; color: var(--accent-strong); font-size: 0.78rem; font-weight: 700; }
.lesson-stats { margin: 0.18rem 0 0; color: var(--muted); font-size: 0.72rem; }
.reader-settings { display: flex; gap: 0.8rem; }
.reader-settings label { color: var(--muted); font-size: 0.7rem; }
.reader-settings select { margin-left: 0.3rem; padding: 0.38rem 1.7rem 0.38rem 0.5rem; border: 1px solid var(--line); border-radius: 0.45rem; background: var(--paper); color: var(--ink); }

.lesson-content { max-width: var(--reading-width); margin: 0 auto; padding: 1.4rem 0 5rem; background: var(--paper); font-size: var(--body-size); }
html[data-font-size="compact"] { --body-size: 0.92rem; --reading-width: 68rem; --text-width: 51rem; }
html[data-font-size="large"] { --body-size: 1.1rem; --reading-width: 74rem; --text-width: 55rem; }

.lesson-content h1,
.lesson-content h2,
.lesson-content h3,
.lesson-content h4 { color: var(--ink); line-height: 1.35; text-wrap: balance; }
.lesson-content h1 { width: 100%; max-width: none; margin: 0 0 1.75rem; font-size: clamp(2rem, 3vw, 2.65rem); letter-spacing: -0.04em; }
.lesson-content > h1.chapter-title {
  display: grid;
  grid-template-columns: minmax(7.5rem, 0.28fr) minmax(0, 1.72fr);
  gap: clamp(1.5rem, 3vw, 3.5rem);
  align-items: end;
  min-height: clamp(10rem, 13vw, 13rem);
  margin-bottom: 2.75rem;
  padding: clamp(1.5rem, 3vw, 2.5rem) 0 2rem;
  border-bottom: 1px solid var(--line);
  font-size: inherit;
  letter-spacing: 0;
}
.chapter-index { display: grid; gap: 0.35rem; align-content: end; color: var(--accent-strong); }
.chapter-index-label { font-size: 0.72rem; font-weight: 700; letter-spacing: 0.08em; }
.chapter-index-number { font-size: clamp(2.5rem, 4vw, 4rem); font-weight: 300; font-variant-numeric: tabular-nums; line-height: 0.92; }
.chapter-title-copy { max-width: none; font-size: clamp(2rem, 3vw, 2.65rem); font-weight: 720; letter-spacing: -0.035em; line-height: 1.24; text-wrap: balance; }
.lesson-content h1 + blockquote { margin: 0 0 3rem; padding: 1.35rem 1.6rem; border: 0; border-radius: 0.75rem; background: linear-gradient(120deg, var(--surface), var(--accent-soft)); font-size: 1.02em; }
.lesson-content h2 { display: grid; grid-template-columns: auto minmax(0, 1fr); gap: 0.8rem; align-items: baseline; margin: 5.25rem 0 1.5rem; font-size: clamp(1.5rem, 2.6vw, 2rem); letter-spacing: -0.025em; }
.section-number { color: var(--accent); font-size: 0.9em; font-weight: 500; }
.section-title { min-width: 0; }
.lesson-content h3 { margin: 3rem 0 1rem; font-size: 1.28rem; }
.lesson-content h4 { margin: 2.15rem 0 0.8rem; font-size: 1.07rem; }
.lesson-content > :is(h2, h3, h4, p:not(.media-holder), ul, ol, blockquote:not(.video-card)) { width: 100%; max-width: var(--text-width); margin-right: auto; margin-left: auto; }
.lesson-content p { max-width: 64rem; margin: 1rem 0; line-height: 1.92; }
.lesson-content > p.chapter-lead { margin-top: -0.35rem; margin-bottom: 2rem; color: var(--ink-soft); font-size: 1.08em; line-height: 1.85; }
.lesson-content strong { color: color-mix(in srgb, var(--ink) 88%, var(--accent)); }
.lesson-content code { padding: 0.08em 0.3em; border-radius: 0.28rem; background: var(--surface-strong); color: var(--accent-strong); font-family: ui-monospace, SFMono-Regular, Consolas, monospace; font-size: 0.92em; overflow-wrap: anywhere; word-break: break-word; }
.lesson-content pre { max-width: 100%; white-space: pre-wrap; overflow-wrap: anywhere; word-break: break-word; }
.lesson-content pre code { padding: 0; background: transparent; }
.lesson-content ol,
.lesson-content ul { margin: 1.25rem 0; padding-left: 1.6rem; }
.lesson-content li { margin: 0.62rem 0; padding-left: 0.25rem; line-height: 1.8; }
.lesson-content li::marker { color: var(--accent); font-weight: 700; }
.lesson-content blockquote { margin: 1.8rem 0; padding: 0.35rem 1.25rem; border-left: 0.22rem solid var(--accent); background: var(--surface); color: var(--ink-soft); }
.lesson-content blockquote > :first-child { margin-top: 0.65rem; }
.lesson-content blockquote > :last-child { margin-bottom: 0.65rem; }
.lesson-content hr { margin: 4rem 0; border: 0; border-top: 1px solid var(--line); }

.media-holder { max-width: none !important; margin: 2.2rem 0 2.7rem !important; }
.media-holder figure { margin: 0; }
.media-holder.media-wide { margin-right: -1.5rem !important; margin-left: -1.5rem !important; }
.media-holder.media-focus { width: min(88%, 58rem); margin-right: auto !important; margin-left: auto !important; }
.media-holder.image-led { margin-top: 2.8rem !important; margin-bottom: 2rem !important; }
.media-holder.image-led + p { max-width: 58rem; margin: -0.7rem auto 3.25rem; color: var(--ink-soft); font-size: 0.86em; line-height: 1.75; }
.lesson-content figure button { display: block; width: 100%; padding: 0; border: 0; border-radius: 0.7rem; background: transparent; cursor: zoom-in; }
.lesson-content img { display: block; width: 100%; height: auto; border: 1px solid color-mix(in srgb, var(--line) 70%, transparent); border-radius: 0.7rem; background: #f0eee8; }
.lesson-content figcaption { margin-top: 0.58rem; color: var(--muted); font-size: 0.74rem; line-height: 1.55; text-align: center; }

.media-pair { display: grid; grid-template-columns: minmax(0, 1.7fr) minmax(12rem, 0.65fr); gap: clamp(1.35rem, 3vw, 2.6rem); align-items: center; margin: 2.5rem 0 3rem; padding: clamp(1rem, 2.4vw, 1.6rem); border: 1px solid var(--line); border-radius: 0.85rem; background: var(--surface); }
.media-pair.image-right { grid-template-columns: minmax(12rem, 0.65fr) minmax(0, 1.7fr); }
.media-pair > p { margin: 0 !important; }
.media-pair .media-holder { width: auto; }
.media-pair.image-right .media-holder { order: 2; }
.media-pair.image-right > p:last-child { order: 1; }
.media-pair > p:last-child { color: var(--ink-soft); font-size: 0.84em; line-height: 1.75; }

.table-responsive { margin: 2rem -1.5rem 2.75rem; border: 1px solid var(--line); border-radius: 0.72rem; background: var(--paper); }
.lesson-content table { width: 100%; border-collapse: collapse; table-layout: auto; font-size: clamp(0.72rem, 0.78vw, 0.83rem); line-height: 1.48; }
.lesson-content thead { background: var(--accent-strong); color: #f7fbf9; }
.lesson-content th,
.lesson-content td { min-width: 0; padding: 0.72rem 0.62rem; border-right: 1px solid var(--line); text-align: left; vertical-align: top; overflow-wrap: anywhere; word-break: normal; }
.lesson-content th:last-child,
.lesson-content td:last-child { border-right: 0; }
.lesson-content tbody tr + tr { border-top: 1px solid var(--line); }
.lesson-content tbody tr:nth-child(even) { background: var(--surface); }

.video-card { display: grid; grid-template-columns: minmax(18rem, 1.2fr) minmax(15rem, 0.8fr); overflow: hidden; margin: 2.25rem 0; padding: 0 !important; border: 1px solid var(--line) !important; border-radius: 0.78rem; background: var(--surface) !important; }
.video-frame { position: relative; aspect-ratio: 16 / 9; background: #101613; }
.video-frame iframe { position: absolute; inset: 0; width: 100%; height: 100%; border: 0; }
.video-copy { align-self: center; padding: 1.15rem 1.25rem; }
.video-copy p { margin: 0.4rem 0; }
.video-copy a { color: var(--accent-strong); font-weight: 700; text-underline-offset: 0.22em; }

.loading-state { display: grid; gap: 0.8rem; padding: 2rem 0; }
.loading-state div { height: 1rem; border-radius: 0.3rem; background: var(--surface-strong); }
.loading-state div:nth-child(2) { width: 88%; }
.loading-state div:nth-child(3) { width: 95%; }
.loading-state div:nth-child(4) { width: 66%; }
.loading-state p { color: var(--muted); font-size: 0.82rem; }
.error-state { padding: 2rem; border: 1px solid #a75050; border-radius: 0.65rem; background: color-mix(in srgb, #a75050 8%, var(--paper)); }

.lesson-footer { display: grid; grid-template-columns: 1fr auto 1fr; align-items: center; gap: 1rem; max-width: var(--reading-width); margin: 1rem auto 0; padding: 1.5rem 0; border-top: 1px solid var(--line); color: var(--muted); font-size: 0.8rem; }
.lesson-footer p { margin: 0; }
.module-step { display: grid; min-width: 0; padding: 0.65rem 0.75rem; border-radius: 0.5rem; text-decoration: none; }
.module-step:hover { background: var(--surface); }
.module-step.next { text-align: right; }
.module-step strong { color: var(--ink-soft); }
.module-step span { overflow: hidden; color: var(--muted); text-overflow: ellipsis; white-space: nowrap; }

.image-dialog { width: min(94vw, 76rem); max-height: 94dvh; padding: 0; border: 1px solid var(--line); border-radius: 0.8rem; background: var(--paper); color: var(--ink); }
.image-dialog::backdrop { background: rgba(7, 15, 12, 0.82); }
.image-dialog figure { margin: 0; padding: 3.5rem 1rem 1rem; }
.image-dialog img { display: block; max-width: 100%; max-height: 78dvh; margin: auto; border-radius: 0.45rem; }
.image-dialog figcaption { padding: 0.75rem 0 0; color: var(--ink-soft); text-align: center; }
.dialog-close { position: absolute; top: 0.75rem; right: 0.75rem; padding: 0.45rem 0.7rem; border: 1px solid var(--line); border-radius: 0.45rem; background: var(--surface); color: var(--ink); cursor: pointer; }

.nav-backdrop { position: fixed; inset: var(--header-height) 0 0; z-index: 18; background: rgba(7, 15, 12, 0.62); }
:focus-visible { outline: 3px solid color-mix(in srgb, var(--accent) 72%, white); outline-offset: 3px; }

@media (max-width: 1180px) {
  .reader-shell { grid-template-columns: 16rem minmax(0, 1fr); }
  .header-inner { grid-template-columns: minmax(14rem, 1fr) minmax(24rem, 30rem); }
  .reading-stage { padding-right: 2rem; padding-left: 2rem; }
  .media-pair { grid-template-columns: minmax(0, 1.55fr) minmax(11rem, 0.55fr); }
  .media-pair.image-right { grid-template-columns: minmax(11rem, 0.55fr) minmax(0, 1.55fr); }
}

@media (max-width: 820px) {
  :root { --header-height: 4.35rem; }
  .header-inner { display: flex; gap: 0.75rem; padding: 0 1rem; }
  .menu-button { display: block; padding: 0.42rem 0.65rem; border: 1px solid var(--line); border-radius: 0.45rem; background: var(--surface); color: var(--ink); }
  .brand-copy strong { font-size: 0.88rem; }
  .brand-copy span { display: none; }
  .course-progress { grid-template-columns: minmax(5rem, 1fr) auto; gap: 0.45rem; margin-left: auto; }
  .progress-copy { display: none; }
  .progress-track { width: clamp(5rem, 24vw, 9rem); }
  .reader-shell { display: block; }
  .course-nav { position: fixed; top: var(--header-height); bottom: 0; left: 0; z-index: 19; width: min(88vw, 22rem); background: var(--canvas); transform: translateX(-102%); visibility: hidden; transition: transform 180ms ease, visibility 0s linear 180ms; }
  .course-nav.open { visibility: visible; transform: translateX(0); transition-delay: 0s; }
  body.menu-open { overflow: hidden; }
  .nav-scroll { max-height: 100%; padding: 1rem; }
  .reading-stage { padding: 1rem clamp(1rem, 4vw, 1.5rem) 3rem; }
  .lesson-intro { display: grid; gap: 1rem; margin-bottom: 0.75rem; }
  .reader-settings { justify-content: space-between; }
  .lesson-content { padding-top: 1.5rem; }
  .lesson-content h1 { font-size: 2rem; }
  .lesson-content > h1.chapter-title { grid-template-columns: 1fr; gap: 0.75rem; min-height: auto; margin-bottom: 2rem; padding: 1.25rem 0 1.5rem; }
  .chapter-index { display: flex; align-items: baseline; gap: 0.5rem; }
  .chapter-index-number { font-size: 1.2rem; font-weight: 700; line-height: 1; }
  .chapter-title-copy { max-width: none; font-size: clamp(1.75rem, 6.8vw, 2.05rem); line-height: 1.3; }
  .lesson-content h2 { margin-top: 4.25rem; }
  .media-holder.media-wide,
  .media-holder.media-focus { width: auto; margin-right: 0 !important; margin-left: 0 !important; }
  .media-pair,
  .video-card { grid-template-columns: 1fr; }
  .media-pair.image-right .media-holder,
  .media-pair.image-right > p:last-child { order: initial; }
  .media-pair > p:last-child { padding: 0.25rem 0.25rem 0.1rem; }
  .table-responsive { margin: 1.6rem 0 2rem; border: 0; background: transparent; }
  .lesson-content table,
  .lesson-content tbody,
  .lesson-content tr,
  .lesson-content td { display: block; width: 100%; }
  .lesson-content thead { display: none; }
  .lesson-content tbody { display: grid; gap: 0.8rem; }
  .lesson-content tbody tr { overflow: hidden; border: 1px solid var(--line) !important; border-radius: 0.65rem; background: var(--paper) !important; }
  .lesson-content td { display: grid; grid-template-columns: minmax(7rem, 38%) minmax(0, 1fr); gap: 0.75rem; padding: 0.68rem 0.75rem; border: 0; border-bottom: 1px solid var(--line); font-size: 0.82rem; }
  .lesson-content td:last-child { border-bottom: 0; }
  .lesson-content td::before { content: attr(data-label); color: var(--accent-strong); font-weight: 700; }
}

@media (max-width: 520px) {
  .brand-copy strong { max-width: 11rem; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
  .progress-count { display: none; }
  .course-progress { grid-template-columns: 1fr; }
  .reading-stage { padding-right: 1rem; padding-left: 1rem; }
  .lesson-content h1 { font-size: 1.72rem; }
  .lesson-content h2 { grid-template-columns: 1fr; gap: 0.15rem; font-size: 1.45rem; }
  .section-number { font-size: 0.75em; }
  .lesson-content p { line-height: 1.84; }
  .reader-settings { display: grid; grid-template-columns: 1fr; }
  .reader-settings label { display: grid; gap: 0.25rem; }
  .reader-settings select { width: 100%; margin: 0; }
  .media-pair { padding: 0.75rem; }
  .lesson-content td { grid-template-columns: 1fr; gap: 0.22rem; }
  .lesson-footer { grid-template-columns: 1fr 1fr; }
  .lesson-footer p { display: none; }
}

@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  *, *::before, *::after { animation-duration: 0.01ms !important; animation-iteration-count: 1 !important; transition-duration: 0.01ms !important; }
}

@media print {
  .site-header, .course-nav, .lesson-intro, .lesson-footer { display: none !important; }
  body, .reader-shell, .reading-stage, .lesson-content { display: block; margin: 0; padding: 0; background: white; color: black; box-shadow: none; }
  .lesson-content { max-width: none; border: 0; font-size: 11pt; }
  .media-pair, .video-card { display: block; border: 0; padding: 0; }
  .video-frame { display: none; }
  .video-copy a::after { content: " (" attr(href) ")"; font-weight: 400; }
}