/* ============================================================
   Matheca — 介绍页
   方向：批改现场。白纸、石墨字、一笔朱红。
   ============================================================ */

:root {
  /* 底色与墨色 */
  --shell:        #f6f7f8;
  --paper:        #ffffff;
  --paper-2:      #fbfbfc;
  --ink:          #15181c;
  --ink-2:        #343a42;
  --muted:        #5f666f;
  --faint:        #656c75;
  --line:         #e5e8eb;
  --line-2:       #d5dae0;

  /* 朱红：红笔、批注、主行动 */
  /* 图纸网格：两档线，只提供质感，不参与信息层级 */
  --grid-fine:    rgba(20, 22, 26, .035);
  --grid-major:   rgba(20, 22, 26, .045);

  --pen:          #b32f24;
  --pen-hover:    #94241a;
  --pen-soft:     #f9ebe8;

  /* 夜间区 */
  --night:        #14171b;
  --night-2:      #1b1f24;
  --night-ink:    #eef0f2;
  --night-muted:  #9ba2ab;
  --night-line:   rgba(255, 255, 255, .11);
  --night-pen:    #f0776a;

  /* 字体 */
  --font: "Segoe UI", system-ui, -apple-system, "PingFang SC", "Microsoft YaHei", "Hiragino Sans GB", sans-serif;
  --font-math: "Cambria Math", "Latin Modern Math", "STIX Two Math", "Times New Roman", "Songti SC", serif;

  /* 间距：4pt 基数 */
  --s1: 4px;  --s2: 8px;  --s3: 12px; --s4: 16px;
  --s5: 20px; --s6: 24px; --s8: 32px; --s10: 40px;
  --s12: 48px; --s16: 64px; --s20: 80px; --s24: 96px; --s30: 120px;

  /* 圆角 */
  --r-xs: 4px; --r-sm: 8px; --r-md: 12px; --r-lg: 16px; --r-xl: 20px; --r-full: 999px;

  /* 投影 */
  --sh-1: 0 1px 2px rgba(20, 22, 26, .05);
  --sh-2: 0 1px 2px rgba(20, 22, 26, .04), 0 10px 26px -12px rgba(20, 22, 26, .16);
  --sh-3: 0 2px 6px rgba(20, 22, 26, .05), 0 22px 48px -20px rgba(20, 22, 26, .22);

  /* 动效 */
  --t-fast: 140ms;
  --t-mid: 240ms;
  --t-slow: 620ms;
  --ease-out: cubic-bezier(.16, .84, .44, 1);
}

/* ---------------------------------------------------------- 基础 */

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

html {
  -webkit-text-size-adjust: 100%;
  scroll-behavior: smooth;
  scroll-padding-top: 84px;
  scrollbar-color: #c6cbd1 transparent;
}

body {
  margin: 0;
  font-family: var(--font);
  font-size: 1rem;
  line-height: 1.7;
  color: var(--ink);
  background-color: var(--shell);
  background-image:
    linear-gradient(to right, var(--grid-fine) 1px, transparent 1px),
    linear-gradient(to bottom, var(--grid-fine) 1px, transparent 1px),
    linear-gradient(to right, var(--grid-major) 1px, transparent 1px),
    linear-gradient(to bottom, var(--grid-major) 1px, transparent 1px);
  background-size: 56px 56px, 56px 56px, 280px 280px, 280px 280px;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}

h1, h2, h3 { margin: 0; line-height: 1.25; font-weight: 600; letter-spacing: -.01em; }
p { margin: 0; }
ul, ol { margin: 0; padding: 0; list-style: none; }
a { color: inherit; text-decoration: none; }
svg { display: block; }

code {
  font-family: ui-monospace, "SF Mono", "Cascadia Mono", Consolas, monospace;
  font-size: .9em;
  background: var(--paper);
  border: 1px solid var(--line);
  border-radius: var(--r-xs);
  padding: .08em .35em;
}

:focus-visible {
  /* 墨色描边在浅底和红色按钮上都看得见；朱红会跟主行动混在一起。
     不要在这里写 border-radius：它会改掉被聚焦元素本身的形状。 */
  outline: 2px solid var(--ink);
  outline-offset: 3px;
}

::selection { background: var(--pen); color: #fff; }

.visually-hidden {
  position: absolute; width: 1px; height: 1px;
  margin: -1px; padding: 0; overflow: hidden;
  clip: rect(0 0 0 0); white-space: nowrap; border: 0;
}

.skip {
  position: fixed; top: -100px; left: 16px; z-index: 100;
  background: var(--ink); color: #fff;
  padding: 10px 16px; border-radius: var(--r-sm);
  font-size: .9rem;
  transition: top var(--t-fast) var(--ease-out);
}
.skip:focus { top: 12px; }

.wrap {
  width: 100%;
  max-width: 1180px;
  margin-inline: auto;
  padding-inline: clamp(20px, 5vw, 48px);
}

/* 数学：真排版，不截图 */
.math {
  font-family: var(--font-math);
  font-size: 1.02em;
  letter-spacing: .01em;
}
.math i { font-style: italic; }
.math sup { font-size: .62em; vertical-align: .42em; line-height: 0; }

/* 中文括号与词不要被行尾拆开 */
.nw { white-space: nowrap; }
.math--lg { font-size: clamp(2rem, 1.4em + 2vw, 3rem); }

/* ---------------------------------------------------------- 按钮 */

.btn {
  --btn-bg: var(--paper);
  --btn-fg: var(--ink);
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--s2);
  min-height: 48px;
  padding: 0 var(--s6);
  font: inherit;
  font-size: .95rem;
  font-weight: 600;
  letter-spacing: .01em;
  color: var(--btn-fg);
  background: var(--btn-bg);
  border: 1px solid transparent;
  border-radius: var(--r-full);
  cursor: pointer;
  white-space: nowrap;
  transition: background-color var(--t-fast) var(--ease-out),
              color var(--t-fast) var(--ease-out),
              border-color var(--t-fast) var(--ease-out),
              box-shadow var(--t-fast) var(--ease-out),
              transform 120ms var(--ease-out);
}
.btn:active { transform: translateY(1px); }

.btn--pen { background: var(--pen); color: #fff; box-shadow: var(--sh-1); }
.btn--pen:hover { background: var(--pen-hover); }

.btn--ink { background: var(--ink); color: #fff; }
.btn--ink:hover { background: #000; }

.btn--line {
  background: transparent;
  color: var(--ink);
  border-color: var(--line-2);
}
.btn--line:hover { background: var(--paper); border-color: var(--ink); }

.btn--sm { min-height: 38px; padding: 0 var(--s5); font-size: .875rem; }
.btn--lg { min-height: 54px; padding: 0 var(--s8); font-size: 1rem; }
.btn svg { flex: none; }

/* ---------------------------------------------------------- 顶栏 */

.topbar {
  position: sticky;
  top: 0;
  z-index: 50;
  background: rgba(246, 247, 248, .82);
  backdrop-filter: saturate(160%) blur(14px);
  -webkit-backdrop-filter: saturate(160%) blur(14px);
  border-bottom: 1px solid transparent;
  transition: border-color var(--t-mid) var(--ease-out), background-color var(--t-mid) var(--ease-out);
}
.topbar.is-stuck {
  border-bottom-color: var(--line);
  background: rgba(246, 247, 248, .94);
}

.topbar__inner {
  display: flex;
  align-items: center;
  gap: var(--s6);
  min-height: 68px;
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: var(--s2);
  color: var(--ink);
  margin-right: auto;
}
.brand__mark { transition: transform var(--t-mid) var(--ease-out); }
.brand:hover .brand__mark { transform: rotate(-6deg); }
.brand__name {
  font-size: 1.0625rem;
  font-weight: 650;
  letter-spacing: -.015em;
}

.nav {
  display: flex;
  align-items: center;
  gap: var(--s1);
}
.nav a {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 9px 12px;
  border-radius: var(--r-sm);
  font-size: .9rem;
  color: var(--ink-2);
  transition: background-color var(--t-fast) var(--ease-out), color var(--t-fast) var(--ease-out);
}
.nav a:hover { background: rgba(20, 22, 26, .055); color: var(--ink); }
.nav__gh { color: var(--muted); }
.nav__gh svg { opacity: .8; }
.nav .nav__cta {
  margin-left: var(--s3);
  min-height: 40px;
  padding: 0 var(--s5);
  color: #fff;
}
.nav .nav__cta:hover { color: #fff; background: var(--pen-hover); }

/* 只在窄屏出现的软换行 */
.smBr { display: none; }

.navToggle {
  display: none;
  align-items: center;
  justify-content: center;
  width: 44px; height: 44px;
  padding: 0;
  background: var(--paper);
  border: 1px solid var(--line);
  border-radius: var(--r-sm);
  cursor: pointer;
}
.navToggle span { display: grid; gap: 5px; width: 16px; }
.navToggle i {
  display: block; height: 1.5px; width: 16px; background: var(--ink);
  transition: transform var(--t-mid) var(--ease-out), opacity var(--t-fast);
}
.navToggle[aria-expanded="true"] i:first-child { transform: translateY(3.25px) rotate(35deg); }
.navToggle[aria-expanded="true"] i:last-child { transform: translateY(-3.25px) rotate(-35deg); }

/* ---------------------------------------------------------- Hero */

.hero { padding-block: clamp(48px, 7vw, 96px) clamp(48px, 6vw, 88px); }

/* 首屏之后的第一段不需要再撑一次大留白 */
.hero + .section,
.forwho + .section { padding-top: clamp(40px, 5vw, 72px); }

.hero__grid {
  display: grid;
  grid-template-columns: minmax(0, 1.02fr) minmax(0, .98fr);
  gap: clamp(32px, 5vw, 72px);
  align-items: center;
}

.hero__copy > * { animation: rise var(--t-slow) var(--ease-out) both; }
.hero__copy > *:nth-child(1) { animation-delay: 40ms; }
.hero__copy > *:nth-child(2) { animation-delay: 90ms; }
.hero__copy > *:nth-child(3) { animation-delay: 150ms; }
.hero__copy > *:nth-child(4) { animation-delay: 210ms; }
.hero__copy > *:nth-child(5) { animation-delay: 270ms; }
.hero__copy > *:nth-child(6) { animation-delay: 330ms; }

@keyframes rise {
  from { opacity: 0; transform: translateY(14px); }
  to   { opacity: 1; transform: none; }
}

.hero__title {
  margin-block: clamp(16px, 2.4vw, 24px) 0;
  font-size: clamp(3rem, 1.5rem + 5.4vw, 5.25rem);
  font-weight: 620;
  letter-spacing: -.04em;
  line-height: .96;
}

.hero__tagline {
  margin-top: clamp(14px, 2vw, 20px);
  font-size: clamp(1.4rem, 1.1rem + 1.35vw, 2rem);
  font-weight: 600;
  line-height: 1.35;
  letter-spacing: -.015em;
  color: var(--ink);
}
/* 红笔下划线：手画的那一笔 */
.mark {
  white-space: nowrap;
  background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 200 12' preserveAspectRatio='none'%3E%3Cpath d='M3 8.6C42 4.2 92 3.3 148 5.3c17 .6 32 1.5 49 2.9' fill='none' stroke='%23c33529' stroke-width='3.4' stroke-linecap='round'/%3E%3C/svg%3E");
  background-repeat: no-repeat;
  background-position: 0 100%;
  background-size: 100% .26em;
  padding-bottom: .1em;
}

.hero__lede {
  margin-top: var(--s5);
  max-width: 34em;
  font-size: 1.0625rem;
  line-height: 1.78;
  color: var(--ink-2);
}

.hero__actions {
  display: flex;
  flex-wrap: wrap;
  gap: var(--s3);
  margin-top: var(--s8);
}

.hero__meta {
  display: flex;
  flex-wrap: wrap;
  gap: var(--s2) var(--s5);
  margin-top: var(--s6);
  font-size: .8125rem;
  color: var(--muted);
}
.hero__meta li { display: flex; align-items: center; gap: var(--s2); }
.hero__meta li::before {
  content: "";
  width: 4px; height: 4px;
  background: var(--line-2);
  border-radius: 50%;
}

/* ---------------------------------------------------------- 校对现场 */

.proof {
  position: relative;
  margin: 0;
  animation: rise var(--t-slow) var(--ease-out) 260ms both;
}

/* 卡片所属的题集：一条能读清的落款 */
.proof__set {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: var(--s4);
  margin-top: var(--s3);
  padding: 10px var(--s4);
  background: var(--paper-2);
  border: 1px solid var(--line);
  border-radius: var(--r-sm);
  font-size: .75rem;
  color: var(--muted);
}
.proof__setTitle { font-weight: 600; color: var(--ink-2); }
.proof__setMeta { font-variant-numeric: tabular-nums; white-space: nowrap; }

.proof__card {
  position: relative;
  background: var(--paper);
  border: 1px solid var(--line);
  border-radius: var(--r-md);
  box-shadow: var(--sh-3);
}

.proof__head {
  display: flex;
  align-items: center;
  gap: var(--s3);
  padding: var(--s4) var(--s5);
  border-bottom: 1px solid var(--line);
}

/* 题号写成文字而不是徽章：第 1 题 */
.proof__qn {
  flex: none;
  font-size: .75rem;
  font-weight: 600;
  letter-spacing: .04em;
  color: var(--muted);
  white-space: nowrap;
}
.proof__qn b {
  font-size: .9375rem;
  font-weight: 650;
  letter-spacing: 0;
  color: var(--ink);
}

/* 卡头的一条分类摘要：年级 · 难度 · 知识点 */
.proof__meta {
  display: flex;
  align-items: baseline;
  gap: 7px;
  margin: 0 auto 0 0;
  font-size: .8125rem;
  line-height: 1.5;
  color: var(--muted);
}
.proof__kp {
  font-size: .875rem;
  font-weight: 600;
  letter-spacing: -.005em;
  color: var(--ink-2);
}
.proof__sep::before { content: "·"; color: var(--faint); }

.proof__stamp {
  margin-left: auto;
  padding: 2px 8px;
  font-size: .6875rem;
  font-weight: 700;
  letter-spacing: .14em;
  color: var(--pen);
  border: 1.5px solid var(--pen);
  border-radius: 3px;
  transform: rotate(-7deg);
  opacity: .92;
  transition: opacity 260ms var(--ease-out), transform 340ms var(--ease-out);
}
/* 脚本可用时，章从「还没盖」的位置落下来；无脚本就一直是盖好的样子 */
.js .proof:not(.is-done) .proof__stamp {
  opacity: 0;
  transform: rotate(-7deg) scale(1.6);
}

.proof__body {
  display: grid;
  grid-template-columns: 104px minmax(0, 1fr);
  gap: var(--s5);
  padding: var(--s5);
}

.scan {
  position: relative;
  align-self: start;
  width: 104px;
  padding: 13px 11px;
  background: linear-gradient(168deg, #f4f5f6, #e6e9ec);
  border: 1px solid var(--line-2);
  border-radius: var(--r-xs);
  display: grid;
  gap: 7px;
  transform: rotate(-1.2deg);
}
.scan__no {
  font-family: var(--font-math);
  font-size: .8125rem;
  line-height: 1;
  color: rgba(20, 22, 26, .38);
}
.scan__line {
  height: 4px;
  width: var(--w, 80%);
  background: rgba(20, 22, 26, .16);
  border-radius: 1px;
}
.scan__c {
  position: absolute;
  width: 7px; height: 7px;
  border: 1.5px solid rgba(20, 22, 26, .28);
}
.scan__c--tl { top: 3px; left: 3px; border-right: 0; border-bottom: 0; }
.scan__c--br { bottom: 3px; right: 3px; border-left: 0; border-top: 0; }

.proof__text { min-width: 0; }

.stem {
  font-size: .9375rem;
  line-height: 1.7;
  color: var(--ink);
}

.parts {
  margin-top: var(--s2);
  display: grid;
  gap: 4px;
  counter-reset: q;
  font-size: .9375rem;
  line-height: 1.65;
  color: var(--ink-2);
}
.parts li {
  position: relative;
  padding-left: 17px;
}
.parts li::before {
  counter-increment: q;
  content: counter(q) ".";
  position: absolute;
  left: 0; top: 0;
  font-variant-numeric: tabular-nums;
  color: var(--faint);
}
.proof__cap {
  margin-top: var(--s3);
  font-size: .6875rem;
  color: var(--faint);
  text-align: right;
  letter-spacing: .02em;
}

/* ---------------------------------------------------------- 写给谁 */

.forwho {
  border-block: 1px solid var(--line);
  background: rgba(255, 255, 255, .55);
}
.forwho__list {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  margin: 0;
}
.forwho__list > div {
  padding: var(--s6) var(--s6) var(--s6) 0;
}
.forwho__list > div + div {
  padding-left: var(--s8);
  border-left: 1px solid var(--line);
}
.forwho dt {
  margin-bottom: var(--s2);
  font-size: .75rem;
  font-weight: 600;
  letter-spacing: .1em;
  color: var(--pen);
}
.forwho dd {
  margin: 0;
  font-size: .9375rem;
  line-height: 1.7;
  color: var(--ink-2);
  max-width: 30em;
}

/* ---------------------------------------------------------- 区块通用 */

.section { padding-block: clamp(64px, 8.5vw, 120px); }

/* 能力清单单独一段白面，长页面里给一个章节感 */
.section--paper { background: var(--paper); }

.head {
  max-width: 44rem;
  margin-bottom: clamp(32px, 5vw, 56px);
}
.head--night { max-width: 46rem; }

.h2 {
  font-size: clamp(1.75rem, 1.2rem + 2.3vw, 2.75rem);
  font-weight: 620;
  letter-spacing: -.028em;
  line-height: 1.22;
}

.lede {
  margin-top: var(--s4);
  font-size: 1.0625rem;
  line-height: 1.75;
  color: var(--muted);
  max-width: 38em;
}

/* ---------------------------------------------------------- 三段流程 */

.flow {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: clamp(20px, 3vw, 40px);
}

.flow__step {
  display: flex;
  flex-direction: column;
}

.flow__art {
  position: relative;
  height: 244px;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: flex-end;
  gap: var(--s4);
  margin-bottom: var(--s6);
}

/* 阶段一：一张拍歪的照片 */
.art-photo {
  position: relative;
  width: 140px; height: 186px;
  padding: 18px 16px;
  display: grid;
  align-content: start;
  gap: 9px;
  background: var(--paper);
  border: 1px solid var(--line);
  border-radius: var(--r-xs);
  box-shadow: var(--sh-2);
  transform: rotate(-3.2deg);
  overflow: hidden;
}
.art-photo__line {
  height: 4px;
  width: var(--w, 80%);
  background: rgba(20, 22, 26, .16);
  border-radius: 1px;
}
.art-photo__glare {
  position: absolute;
  inset: -30% -60% auto auto;
  width: 90px; height: 240px;
  background: linear-gradient(100deg, rgba(255,255,255,0), rgba(255,255,255,.9));
  transform: rotate(18deg);
}

/* 阶段二：机器稿与红笔 */
/* 阶段二：机器稿与改后的同一页，并排放着 */
.draft {
  display: flex;
  align-items: center;
  gap: 9px;
}
.draft__sheet {
  display: grid;
  align-content: start;
  gap: 11px;
  width: 116px;
  height: 152px;
  padding: 16px 14px;
  background: var(--paper);
  border: 1px solid var(--line);
  border-radius: 4px;
}
.draft__sheet--draft { box-shadow: var(--sh-1); transform: rotate(-2deg); }
.draft__sheet--final { box-shadow: var(--sh-2); }
.draft__line {
  display: block;
  height: 4px;
  width: var(--w, 76%);
  border-radius: 1px;
  background: rgba(20, 22, 26, .15);
}
/* 被机器认错的那一行：划掉，改后的那一行变成实心墨 */
.draft__line--cut { position: relative; background: rgba(20, 22, 26, .08); }
.draft__line--cut::after {
  content: "";
  position: absolute;
  inset: 50% -4px auto -4px;
  height: 1.5px;
  border-radius: 1px;
  background: var(--pen);
  transform: rotate(-1.6deg);
}
.draft__line--ink { background: var(--ink-2); }
/* 两页之间的一道细箭头，只用线，不抢红 */
.draft__arrow {
  position: relative;
  flex: none;
  width: 18px;
  height: 1px;
  background: var(--muted);
  opacity: .55;
}
.draft__arrow::after {
  content: "";
  position: absolute;
  right: 0;
  top: -2px;
  width: 5px;
  height: 5px;
  border-top: 1px solid var(--muted);
  border-right: 1px solid var(--muted);
  transform: rotate(45deg);
}

/* 阶段三：成卷 */
.art-paper {
  position: relative;
  width: 156px; height: 200px;
  padding: 14px 16px;
  display: grid;
  align-content: start;
  gap: 8px;
  background: var(--paper);
  border: 1px solid var(--line);
  border-radius: var(--r-xs);
  box-shadow: var(--sh-2);
}
.art-paper__head {
  height: 14px;
  margin-bottom: 3px;
  background: linear-gradient(90deg, var(--ink) 0 40%, transparent 40% 56%, rgba(20,22,26,.16) 56% 100%);
  border-radius: 1px;
  opacity: .9;
}
.art-paper__line {
  height: 3px;
  width: var(--w, 90%);
  background: rgba(20, 22, 26, .17);
  border-radius: 1px;
}
.art-paper__foot {
  position: absolute;
  left: 14px; right: 14px; bottom: 12px;
  height: 1px;
  background: var(--line-2);
}

.art-chip {
  padding: 3px 10px;
  font-size: .6875rem;
  font-variant-numeric: tabular-nums;
  color: var(--muted);
  background: var(--paper-2);
  border: 1px solid var(--line);
  border-radius: var(--r-full);
  white-space: nowrap;
}
.art-chip--pen { color: var(--pen); border-color: #efc9c3; background: var(--pen-soft); }

.flow__title {
  display: flex;
  align-items: center;
  gap: var(--s2);
  font-size: 1.125rem;
  font-weight: 650;
  letter-spacing: -.01em;
}
.flow__n {
  display: grid;
  place-items: center;
  width: 22px; height: 22px;
  flex: none;
  font-size: .6875rem;
  font-weight: 700;
  color: var(--pen);
  border: 1px solid currentColor;
  border-radius: 50%;
  opacity: .9;
}

.flow__text {
  margin-top: var(--s2);
  padding-left: 32px;
  font-size: 1rem;
  line-height: 1.72;
  color: var(--muted);
}

/* ---------------------------------------------------------- 功能：bento */

.bento {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: var(--s4);
}

.tile {
  display: flex;
  flex-direction: column;
  gap: var(--s2);
  padding: var(--s5) 0 var(--s6);
  border-top: 1px solid var(--line);
}

.tile--wide { grid-column: span 2; }

.tile__flag {
  display: inline-block;
  margin-left: 10px;
  padding: 1px 7px;
  font-size: .6875rem;
  font-weight: 600;
  color: var(--pen);
  background: var(--pen-soft);
  border-radius: var(--r-xs);
  white-space: nowrap;
  vertical-align: .12em;
}

.tile__title {
  font-size: 1.125rem;
  font-weight: 650;
  letter-spacing: -.01em;
}
.tile--wide .tile__title { font-size: clamp(1.25rem, 1rem + .6vw, 1.5rem); }

.tile__text {
  font-size: 1rem;
  line-height: 1.72;
  color: var(--muted);
}

.tile--note {
  grid-column: span 3;
  display: grid;
  grid-template-columns: minmax(0, .28fr) minmax(0, .72fr);
  align-items: center;
  gap: clamp(20px, 3.4vw, 48px);
  padding-block: var(--s8);
}
.tile__math {
  padding-right: clamp(20px, 3vw, 40px);
  border-right: 1px solid var(--line);
  color: var(--ink);
}
.tile--note .tile__text { max-width: 36em; }

/* ---------------------------------------------------------- 开始使用 */

/* 五步排成一行：五张一样宽的白纸面板，浮在草稿上 */
.steps {
  display: grid;
  grid-template-columns: repeat(5, minmax(0, 1fr));
  gap: 14px;
}

.step {
  display: flex;
  flex-direction: column;
  gap: var(--s2);
  padding: var(--s6) var(--s5);
  border: 1px solid var(--line);
  border-radius: 16px;
  background: var(--paper);
  box-shadow: var(--sh-2);
}
.step__n {
  font-size: .6875rem;
  font-weight: 700;
  letter-spacing: .1em;
  font-variant-numeric: tabular-nums;
  color: var(--ink);
}
.step__title {
  font-size: 1rem;
  font-weight: 650;
}
.step__text {
  font-size: .875rem;
  line-height: 1.7;
  color: var(--ink-2);
}
.step__tag {
  margin-top: auto;
  padding-top: 14px;
  font-size: .6875rem;
  color: var(--faint);
  font-variant-numeric: tabular-nums;
}

.pairing {
  margin-top: clamp(32px, 4vw, 48px);
  padding: clamp(24px, 3.4vw, 40px);
  background: var(--paper);
  border: 1px solid var(--line);
  border-radius: var(--r-md);
  display: grid;
  grid-template-columns: minmax(0, .55fr) minmax(0, 1.45fr);
  gap: clamp(24px, 4vw, 56px);
}

.pairing__head {
  display: flex;
  flex-direction: column;
  gap: var(--s3);
  align-items: flex-start;
  align-self: center;
}
.pairing__title { font-size: 1.1875rem; font-weight: 650; }
.pairing__badge {
  padding: 2px 9px;
  font-size: .6875rem;
  font-weight: 600;
  color: var(--muted);
  border: 1px solid var(--line-2);
  border-radius: var(--r-full);
}

.pairing__steps {
  display: grid;
  gap: var(--s3);
  counter-reset: p;
  font-size: 1rem;
  line-height: 1.7;
  color: var(--ink-2);
}
.pairing__steps li {
  display: grid;
  grid-template-columns: 20px 1fr;
  gap: var(--s2);
}
.pairing__steps li::before {
  counter-increment: p;
  content: counter(p);
  font-size: .75rem;
  font-weight: 700;
  color: var(--pen);
  padding-top: .18em;
  font-variant-numeric: tabular-nums;
}

.pairing__note {
  grid-column: 2;
  width: 100%;
  margin-top: 0;
  padding-top: var(--s3);
  border-top: 1px dashed var(--line-2);
  font-size: .8125rem;
  color: var(--muted);
  line-height: 1.7;
}

/* ---------------------------------------------------------- 边界（夜间） */

.section--night {
  background: var(--night);
  color: var(--night-ink);
  background-image:
    radial-gradient(900px 420px at 12% 0%, rgba(255, 255, 255, .05), transparent 70%);
}
.section--night .h2 { color: #fff; }
.section--night .lede { color: var(--night-muted); }

.limits {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 0 clamp(32px, 5vw, 72px);
}

.limit {
  display: grid;
  grid-template-columns: 26px minmax(0, 1fr);
  gap: var(--s3);
  padding-block: var(--s6);
  border-top: 1px solid var(--night-line);
}
.limit:nth-child(-n + 2) { border-top-color: rgba(255, 255, 255, .2); }

.limit__n {
  font-size: .75rem;
  font-weight: 700;
  font-variant-numeric: tabular-nums;
  color: var(--night-pen);
  padding-top: .35em;
}
.limit h3 {
  font-size: 1.0625rem;
  font-weight: 600;
  color: #fff;
  margin-bottom: 6px;
}
.limit p {
  font-size: 1rem;
  line-height: 1.72;
  color: var(--night-muted);
}

/* ---------------------------------------------------------- 收束 */

.cta {
  padding-block: clamp(72px, 9vw, 128px);
  background: var(--paper);
  border-top: 1px solid var(--line);
}
.cta__inner {
  display: grid;
  grid-template-columns: minmax(0, 1.1fr) minmax(0, .9fr);
  align-items: center;
  gap: clamp(32px, 5vw, 80px);
}
.cta__copy { display: grid; gap: var(--s5); justify-items: start; }

.cta__title {
  font-size: clamp(1.9rem, 1.2rem + 2.8vw, 3.1rem);
  font-weight: 620;
  letter-spacing: -.035em;
  line-height: 1.14;
  max-width: 16em;
}
.cta__text {
  max-width: 34em;
  font-size: 1.0625rem;
  line-height: 1.75;
  color: var(--muted);
}
.cta__actions {
  display: flex;
  flex-wrap: wrap;
  gap: var(--s3);
  margin-top: var(--s3);
}

/* 仓库卡片：页面最后一屏的落款 */
.repo {
  padding: var(--s5) var(--s5) var(--s5);
  background: var(--night);
  border-radius: var(--r-md);
  box-shadow: var(--sh-3);
  color: var(--night-ink);
}
.repo__bar {
  display: flex;
  align-items: center;
  gap: var(--s3);
  padding-bottom: var(--s3);
  border-bottom: 1px solid var(--night-line);
}
.repo__dots { display: flex; gap: 5px; }
.repo__dots i {
  width: 7px; height: 7px;
  border-radius: 50%;
  background: rgba(255, 255, 255, .18);
}
.repo__path {
  font-family: ui-monospace, "SF Mono", "Cascadia Mono", Consolas, monospace;
  font-size: .75rem;
  color: #c3cad1;
}
.repo__tag {
  margin-left: auto;
  padding: 1px 8px;
  font-size: .6875rem;
  color: var(--night-pen);
  border: 1px solid rgba(240, 119, 106, .4);
  border-radius: var(--r-full);
  font-variant-numeric: tabular-nums;
}
.repo__cmd {
  margin-top: var(--s4);
  font-family: ui-monospace, "SF Mono", "Cascadia Mono", Consolas, monospace;
  font-size: .75rem;
  line-height: 1.6;
  color: #e2e6ea;
  overflow-wrap: anywhere;
}
.repo__cmd span { color: var(--night-pen); }
.repo__tree {
  margin-top: var(--s4);
  display: grid;
  gap: 7px;
}
.repo__tree li {
  display: grid;
  grid-template-columns: 82px minmax(0, 1fr);
  gap: var(--s3);
  align-items: baseline;
  font-size: .75rem;
  color: var(--night-muted);
}
.repo__tree code {
  background: rgba(255, 255, 255, .07);
  border-color: rgba(255, 255, 255, .07);
  color: #e6e9ec;
  text-align: center;
}

/* ---------------------------------------------------------- 页脚 */

/* 结尾段之后的一行底注：品牌与链接在顶栏、结尾段都已出现，这里只留免责句 */
.footer {
  background: var(--paper);
  border-top: 1px solid var(--line);
  padding-block: var(--s6) var(--s8);
}
.footer__note {
  margin: 0;
  max-width: 62em;
  font-size: .75rem;
  line-height: 1.7;
  color: var(--faint);
}

/* ---------------------------------------------------------- 入场 */

/* 入场：只有确定 JS 可用时才先藏起来，脚本失效时内容照常可读 */
.js [data-reveal] {
  opacity: 0;
  transform: translateY(9px);
  transition: opacity 480ms var(--ease-out), transform 480ms var(--ease-out);
}
.js [data-reveal].is-visible,
.js [data-reveal].is-in { opacity: 1; transform: none; }

/* 同一行内按列错开，入场像被依次放下 */
.js .bento [data-reveal]:nth-child(3n + 2) { transition-delay: 45ms; }
.js .bento [data-reveal]:nth-child(3n + 3) { transition-delay: 90ms; }

/* ---------------------------------------------------------- 响应式 */

@media (max-width: 1080px) {
  .steps { grid-template-columns: minmax(0, 1fr); gap: var(--s3); }
  .step { padding: var(--s5) var(--s4); }
  .step__text { font-size: 1rem; }
}

@media (max-width: 960px) {
  html { scroll-padding-top: 76px; }

  .hero__grid { grid-template-columns: minmax(0, 1fr); }
  .proof { max-width: 560px; }

  .bento { grid-template-columns: repeat(2, minmax(0, 1fr)); }
  .tile--note { grid-column: span 2; }
  .tile--wide { grid-column: span 2; }

  .cta__inner { grid-template-columns: minmax(0, 1fr); gap: var(--s10); }
  .repo { max-width: 520px; }

  .pairing { grid-template-columns: minmax(0, 1fr); gap: var(--s5); }
  .pairing__note { grid-column: 1; }

  .flow { gap: var(--s4); }
  .flow__art { height: 214px; }
  .art-photo { width: 118px; height: 158px; padding: 14px 12px; }
  .art-paper { width: 132px; height: 172px; padding: 12px 14px; }

  .limits { grid-template-columns: minmax(0, 1fr); }
  .limit:nth-child(2) { border-top-color: var(--night-line); }
  .limit:nth-child(-n + 2) { border-top-color: var(--night-line); }
  .limit:first-child { border-top-color: rgba(255, 255, 255, .2); }
}

@media (max-width: 860px) {
  .navToggle { display: inline-flex; }

  .nav {
    position: absolute;
    top: 100%;
    left: 0;
    right: 0;
    display: none;
    flex-direction: column;
    align-items: stretch;
    gap: 2px;
    padding: var(--s3) clamp(20px, 5vw, 48px) var(--s5);
    background: var(--shell);
    border-bottom: 1px solid var(--line);
    box-shadow: var(--sh-2);
  }
  .nav.is-open { display: flex; }
  .nav a { padding: 12px 8px; font-size: 1rem; border-radius: var(--r-sm); }
  .nav__gh { margin-top: var(--s2); border-top: 1px solid var(--line); padding-top: var(--s4) !important; }
  .nav__cta { margin: var(--s3) 0 0; }

}

@media (max-width: 760px) {

  .flow { grid-template-columns: minmax(0, 1fr); gap: var(--s8); }
  .flow__art { height: 210px; }
  .art-photo { width: 140px; height: 186px; padding: 18px 16px; }
  .art-paper { width: 156px; height: 200px; padding: 14px 16px; }

  .forwho__list { grid-template-columns: minmax(0, 1fr); }
  .forwho__list > div { padding: var(--s5) 0; }
  .forwho__list > div + div {
    padding-left: 0;
    border-left: 0;
    border-top: 1px solid var(--line);
  }
}

@media (max-width: 640px) {
  .smBr { display: block; }

  .hero { padding-block: var(--s8) var(--s12); }
  .hero__title { letter-spacing: -.04em; }
  .hero__lede { font-size: 1rem; }
  .hero__meta {
    display: grid;
    grid-template-columns: repeat(2, minmax(0, 1fr));
    gap: 4px var(--s4);
  }
  .hero__meta li::before { display: none; }

  .proof__set { flex-direction: column; gap: 2px; }
  .proof__body { grid-template-columns: minmax(0, 1fr); }
  .scan { display: none; }
  .proof__cap { text-align: left; }

  .bento { grid-template-columns: minmax(0, 1fr); }
  .tile--wide, .tile--note { grid-column: span 1; }
  .tile--note { grid-template-columns: minmax(0, 1fr); gap: var(--s4); }
  .tile__math {
    padding-right: 0;
    padding-bottom: var(--s3);
    border-right: 0;
    border-bottom: 1px solid var(--line);
    text-align: left;
  }

  /* 手机上不再把每步的顶线加粗成黑杠：那会让五步看起来像五条分隔带 */

  .repo__tree li { grid-template-columns: 76px minmax(0, 1fr); }

  .cta__actions .btn { flex: 1 1 100%; }
}

@media (max-width: 380px) {
  .hero__actions { flex-direction: column; align-items: stretch; }
  .hero__actions .btn { width: 100%; }
}

/* ---------------------------------------------------------- 减少动态 */

@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  *, *::before, *::after {
    animation-duration: .01ms !important;
    animation-delay: 0ms !important;
    transition-duration: .01ms !important;
    transition-delay: 0ms !important;
  }
  .js [data-reveal] { opacity: 1; transform: none; }
  .js .proof:not(.is-done) .proof__stamp { opacity: .92; transform: rotate(-7deg); }
}

/* deploy-check 2026-10-23T08:49:08Z */