/* 第3套 zh · 课堂讲义 / 章节编号长栏 */
:root {
  --ink: #1F3A5F;
  --ink-soft: #334863;
  --gold: #C4A574;
  --gold-deep: #A88854;
  --paper: #FBF7F0;
  --sheet: #FFFCF6;
  --muted: #5C6573;
  --rule: rgba(31, 58, 95, 0.14);
  --col: 750px;
  --serif: "Source Han Serif SC", "Noto Serif SC", "Songti SC", SimSun, Georgia, serif;
  --sans: "Source Han Sans SC", "Noto Sans SC", "PingFang SC", "Microsoft YaHei", sans-serif;
}

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

html {
  scroll-behavior: auto;
  background: var(--paper);
}

body {
  margin: 0;
  color: var(--ink);
  background: var(--paper);
  font-family: var(--serif);
  font-size: 18px;
  line-height: 1.88;
  min-height: 100vh;
}

img,
svg {
  max-width: 100%;
  vertical-align: middle;
}

a {
  color: var(--ink);
  text-underline-offset: 3px;
}

a:hover {
  color: var(--gold-deep);
}

.wrap {
  width: min(var(--col), calc(100% - 36px));
  margin: 0 auto;
}

.sheet-head {
  background: var(--sheet);
  border-bottom: 2px solid var(--ink);
}

.sheet-head .wrap {
  padding: 1.15rem 0 0;
}

.course-meta {
  display: flex;
  justify-content: space-between;
  gap: 0.75rem;
  margin: 0 0 0.7rem;
  font-family: var(--sans);
  font-size: 12px;
  letter-spacing: 0.18em;
  color: var(--muted);
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: 0.7rem;
  text-decoration: none;
  color: var(--ink);
  font-family: var(--sans);
  font-size: 1.7rem;
  font-weight: 700;
  letter-spacing: 0.14em;
  line-height: 1.1;
}

.brand:hover {
  color: var(--ink);
}

.brand svg {
  width: 34px;
  height: 34px;
  flex-shrink: 0;
}

.brand small {
  display: block;
  margin-top: 0.28rem;
  font-size: 12px;
  letter-spacing: 0.2em;
  font-weight: 600;
  color: var(--gold-deep);
}

.sheet-head nav {
  display: flex;
  flex-wrap: wrap;
  gap: 0.35rem 1.5rem;
  margin-top: 0.95rem;
  padding: 0.7rem 0 0.85rem;
  border-top: 1px solid var(--gold);
  font-family: var(--sans);
}

.sheet-head nav a {
  text-decoration: none;
  color: var(--ink-soft);
  font-size: 15px;
  letter-spacing: 0.12em;
  padding-bottom: 3px;
  border-bottom: 2px solid transparent;
}

.sheet-head nav a:hover,
.sheet-head nav a.is-active {
  color: var(--ink);
  border-bottom-color: var(--gold);
}

.opening {
  padding: 2.35rem 0 1.55rem;
}

.kicker {
  margin: 0 0 0.65rem;
  font-family: var(--sans);
  font-size: 12px;
  font-weight: 700;
  letter-spacing: 0.28em;
  color: var(--gold-deep);
}

.opening h1,
.lesson h2 {
  font-weight: 700;
  letter-spacing: 0.02em;
  color: var(--ink);
}

.opening h1 {
  margin: 0 0 1.05rem;
  font-size: clamp(1.7rem, 4.6vw, 2.15rem);
  line-height: 1.38;
}

.lede p:first-of-type {
  font-size: 1.06em;
}

p {
  margin: 0 0 1rem;
}

.byline {
  display: flex;
  flex-wrap: wrap;
  gap: 0.4rem 1.25rem;
  margin: 0 0 1.15rem;
  padding: 0.7rem 0 0;
  border-top: 1px solid var(--gold);
  font-family: var(--sans);
  font-size: 13px;
  letter-spacing: 0.06em;
  color: var(--muted);
}

.take {
  display: flex;
  flex-wrap: wrap;
  gap: 0.7rem;
  margin: 1.15rem 0 0.35rem;
}

.take a {
  display: inline-flex;
  align-items: center;
  gap: 0.45rem;
  padding: 0.55rem 1.05rem;
  text-decoration: none;
  font-family: var(--sans);
  font-size: 15px;
  letter-spacing: 0.06em;
  border: 1px solid var(--ink);
  background: var(--ink);
  color: var(--paper);
}

.take a:hover {
  background: #172b47;
  color: var(--paper);
}

.take a.ghost {
  background: transparent;
  color: var(--ink);
}

.take a.ghost:hover {
  background: var(--ink);
  color: var(--paper);
}

.take svg {
  width: 16px;
  height: 16px;
}

.lesson {
  display: grid;
  grid-template-columns: 3.4rem minmax(0, 1fr);
  column-gap: 1.35rem;
  padding: 2.15rem 0 0.45rem;
  border-top: 1px solid var(--gold);
}

.chap-no {
  margin: 0;
  padding-top: 0.15rem;
  color: var(--gold);
  font-family: var(--sans);
  font-size: 1.25rem;
  font-weight: 700;
  letter-spacing: 0.14em;
  line-height: 1.2;
  font-variant-numeric: tabular-nums;
}

.lesson h2 {
  margin: 0 0 0.95rem;
  font-size: clamp(1.28rem, 3.4vw, 1.52rem);
  line-height: 1.4;
}

.lesson h3 {
  margin: 1.35rem 0 0.55rem;
  font-size: 1.08rem;
  line-height: 1.45;
}

.fn {
  margin: 1.1rem 0 0;
  padding-top: 0.7rem;
  border-top: 1px dotted var(--gold);
  font-size: 14px;
  line-height: 1.7;
  color: var(--muted);
}

.fn span {
  display: block;
  margin: 0 0 0.35rem;
  padding-left: 1.4rem;
  text-indent: -1.4rem;
}

sup {
  font-size: 0.72em;
  font-family: var(--sans);
  color: var(--gold-deep);
}

.excerpt {
  margin: 1.2rem 0 1.15rem;
  padding: 0 0 0 1rem;
  border-left: 2px solid var(--gold);
}

.excerpt .who {
  margin: 0 0 0.4rem;
  font-family: var(--sans);
  font-size: 12px;
  letter-spacing: 0.14em;
  color: var(--ink);
}

.excerpt p:last-child {
  margin-bottom: 0;
}

.notes {
  width: 100%;
  border-collapse: collapse;
  font-size: 16px;
  margin: 0.85rem 0 1.1rem;
}

.notes th,
.notes td {
  border-bottom: 1px solid var(--rule);
  padding: 0.62rem 0.5rem;
  text-align: left;
  vertical-align: top;
}

.notes th {
  font-family: var(--sans);
  font-size: 13px;
  letter-spacing: 0.08em;
  color: var(--ink);
  font-weight: 700;
}

.table-scroll {
  width: 100%;
  overflow-x: auto;
}

.grant {
  margin: 0.95rem 0 1rem;
  padding: 0 0 0.85rem;
  border-bottom: 1px dotted var(--gold);
}

.grant:last-of-type {
  border-bottom: 0;
}

.grant h3 {
  margin: 0 0 0.4rem;
  font-size: 1.05rem;
}

.steps {
  list-style: none;
  margin: 0.5rem 0 1.1rem;
  padding: 0;
  counter-reset: demo;
}

.steps li {
  position: relative;
  margin: 0 0 0.95rem;
  padding: 0 0 0 2.7rem;
}

.steps li::before {
  counter-increment: demo;
  content: counter(demo, decimal-leading-zero);
  position: absolute;
  left: 0;
  top: 0.15rem;
  font-family: var(--sans);
  font-size: 13px;
  font-weight: 700;
  letter-spacing: 0.08em;
  color: var(--gold-deep);
}

.req {
  margin: 0.8rem 0 1.05rem;
  padding: 0.2rem 0 0.2rem 1rem;
  border-left: 2px solid var(--gold);
}

.req li {
  margin: 0 0 0.45rem;
}

.faq {
  margin: 0 0 1.05rem;
  padding: 0 0 0.85rem;
  border-bottom: 1px dotted var(--gold);
}

.faq:last-of-type {
  border-bottom: 0;
}

.faq h3 {
  margin: 0 0 0.4rem;
  font-size: 1.06rem;
}

.faq h3::before {
  content: "问 ";
  font-family: var(--sans);
  font-size: 13px;
  letter-spacing: 0.12em;
  color: var(--gold-deep);
}

.sheet-foot {
  margin-top: 2.2rem;
  padding: 1.35rem 0 2.4rem;
  border-top: 2px solid var(--ink);
  text-align: center;
  font-family: var(--sans);
  font-size: 13px;
  line-height: 1.85;
  color: var(--muted);
}

.sheet-foot .safe {
  margin: 0 0 0.55rem;
  color: var(--ink);
  font-weight: 700;
  letter-spacing: 0.04em;
}

.sheet-foot nav {
  margin: 0.45rem 0 0.65rem;
}

.sheet-foot nav a {
  display: inline-block;
  margin: 0 0.7rem;
  text-decoration: none;
  color: var(--ink);
  letter-spacing: 0.12em;
  border-bottom: 2px solid transparent;
  padding-bottom: 2px;
}

.sheet-foot nav a:hover,
.sheet-foot nav a.is-active {
  border-bottom-color: var(--gold);
}

@media (max-width: 720px) {
  body {
    font-size: 17px;
  }

  .lesson {
    grid-template-columns: 1fr;
    row-gap: 0.25rem;
  }

  .chap-no {
    font-size: 0.95rem;
  }

  .opening h1 {
    font-size: 1.55rem;
  }

  .notes {
    font-size: 15px;
  }

  .course-meta {
    flex-direction: column;
    letter-spacing: 0.1em;
  }
}

@media (max-width: 420px) {
  .wrap {
    width: calc(100% - 24px);
  }

  .brand {
    font-size: 1.4rem;
    letter-spacing: 0.08em;
  }

  .take a {
    width: 100%;
    justify-content: center;
  }

  .sheet-head nav {
    gap: 0.35rem 1rem;
  }
}