/* ============================================================
   响溯 · xiangsudev.cn
   无彩度极简：只有黑白灰，青柠 #ADCF37 仅用于链接下划线
   ============================================================ */

:root {
  --bg:      #FAFAFA;
  --surface: #FFFFFF;
  --ink:     #18181B;
  --ink-2:   #52525B;
  --ink-3:   #8E8E96;
  --line:    #E6E6E9;
  --line-2:  #D4D4D8;

  --lime:    #ADCF37;

  --w:    660px;
  --font: -apple-system, BlinkMacSystemFont, "SF Pro SC", "PingFang SC",
          "Hiragino Sans GB", "Noto Sans SC", "Microsoft YaHei", sans-serif;
  --mono: "SF Mono", ui-monospace, Menlo, Consolas, monospace;
}

* { box-sizing: border-box; }

html {
  scroll-behavior: smooth;
  scroll-padding-top: 76px;
  -webkit-text-size-adjust: 100%;
}

body {
  margin: 0;
  background: var(--bg);
  color: var(--ink);
  font-family: var(--font);
  font-size: 16px;
  line-height: 1.85;
  letter-spacing: 0.01em;
  -webkit-font-smoothing: antialiased;
}

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

h1, h2, h3 {
  margin: 0;
  font-weight: 600;
  line-height: 1.32;
  letter-spacing: -0.012em;
}

code {
  font-family: var(--mono);
  font-size: 0.92em;
}

/* ---------------- 顶栏 ---------------- */
.bar {
  position: sticky;
  top: 0;
  z-index: 20;
  background: rgba(250, 250, 250, 0.86);
  backdrop-filter: saturate(180%) blur(14px);
  -webkit-backdrop-filter: saturate(180%) blur(14px);
  border-bottom: 1px solid var(--line);
}
.bar-in {
  max-width: var(--w);
  margin: 0 auto;
  padding: 0 28px;
  height: 60px;
  display: flex;
  align-items: center;
  gap: 16px;
}
.mark { font-size: 15px; font-weight: 600; }
.bar nav {
  margin-left: auto;
  display: flex;
  gap: 22px;
  font-size: 14.5px;
}
.bar nav a { color: var(--ink-2); transition: color 0.18s ease; }
.bar nav a:hover { color: var(--ink); }

/* ---------------- 版面 ---------------- */
.wrap {
  max-width: var(--w);
  margin: 0 auto;
  padding: 0 28px;
}
main { padding: 76px 0 104px; }

.crumb {
  margin: 0 0 24px;
  font-size: 14px;
  color: var(--ink-3);
}
.crumb a { transition: color 0.18s ease; }
.crumb a:hover { color: var(--ink); }

h1 { font-size: 38px; letter-spacing: -0.028em; }
.lead {
  margin: 22px 0 0;
  font-size: 17px;
  color: var(--ink-2);
}

.block {
  margin-top: 68px;
  padding-top: 46px;
  border-top: 1px solid var(--line);
}
.block h2 { font-size: 20px; margin-bottom: 24px; }

.note {
  margin: 18px 0 0;
  font-size: 14px;
  color: var(--ink-3);
}

/* 青柠下划线链接 */
.link {
  text-decoration: underline;
  text-decoration-color: var(--lime);
  text-decoration-thickness: 2px;
  text-underline-offset: 4px;
  transition: text-decoration-color 0.18s ease;
}
.link:hover { text-decoration-color: var(--ink); }

/* ---------------- 在做的事 ---------------- */
.item h3 { font-size: 19px; }
.item > p {
  margin: 14px 0 0;
  color: var(--ink-2);
}
.item .meta {
  margin-top: 12px;
  font-size: 14px;
  color: var(--ink-3);
}

/* ---------------- 条目列表 ---------------- */
.plain { list-style: none; margin: 0; padding: 0; }
.plain li {
  padding: 19px 0;
  border-bottom: 1px solid var(--line);
  color: var(--ink-2);
}
.plain li:last-child { border-bottom: 0; padding-bottom: 0; }
.plain li b {
  color: var(--ink);
  font-weight: 600;
  margin-right: 10px;
}

/* ---------------- 流程 ---------------- */
.flow-line {
  margin: 0;
  font-family: var(--mono);
  font-size: 13.5px;
  line-height: 2.2;
  color: var(--ink-2);
}

/* ---------------- 渐隐阶梯演示 ---------------- */
.demo-line {
  margin: 0;
  font-size: 24px;
  font-weight: 600;
  line-height: 2;
  letter-spacing: 0.04em;
}
.demo-line .w {
  display: inline-block;
  position: relative;
  transition: color 0.28s ease;
}
/* L1 通读 */
.demo-line[data-level="1"] .w { color: var(--ink); }

/* L2 遮重点词 */
.demo-line[data-level="2"] .w[data-r="key"] { color: transparent; }
.demo-line[data-level="2"] .w[data-r="key"]::after {
  content: "";
  position: absolute;
  left: 6%; right: 6%;
  top: 57%;
  height: 2px;
  border-radius: 1px;
  background: var(--line-2);
}

/* L3 只留首字 */
.demo-line[data-level="3"] .w { color: transparent; }
.demo-line[data-level="3"] .w::after {
  content: "";
  position: absolute;
  left: 14%; right: 14%;
  top: 57%;
  height: 2px;
  border-radius: 1px;
  background: var(--line);
}
.demo-line[data-level="3"] .w[data-r="head"] { color: var(--ink); }
.demo-line[data-level="3"] .w[data-r="head"]::after { display: none; }

/* L4 全脱稿 */
.demo-line[data-level="4"] .w { color: transparent; }
.demo-line[data-level="4"] .w::after {
  content: "";
  position: absolute;
  left: 14%; right: 14%;
  top: 57%;
  height: 2px;
  border-radius: 1px;
  background: var(--line);
}

.demo-source {
  margin: 16px 0 0;
  font-size: 14px;
  color: var(--ink-3);
}

.ladder {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin-top: 28px;
}
.ladder-btn {
  appearance: none;
  cursor: pointer;
  font-family: inherit;
  font-size: 13.5px;
  padding: 7px 15px;
  border-radius: 999px;
  border: 1px solid var(--line);
  background: transparent;
  color: var(--ink-2);
  transition: color 0.18s ease, border-color 0.18s ease,
              background 0.18s ease;
}
.ladder-btn:hover { border-color: var(--line-2); color: var(--ink); }
.ladder-btn.is-active {
  background: var(--ink);
  border-color: var(--ink);
  color: var(--bg);
}

.demo-hint {
  margin: 18px 0 0;
  font-size: 14px;
  color: var(--ink-3);
  min-height: 1.85em;
}

.badge {
  display: inline-block;
  margin-left: 12px;
  font-size: 13px;
  font-weight: 400;
  color: var(--ink-3);
  letter-spacing: 0;
}

/* ---------------- 下载 ---------------- */
.cta-line { margin: 0; color: var(--ink-2); }
.cta-mail { margin: 16px 0 0; font-size: 15px; }

/* ---------------- 页脚 ---------------- */
.foot {
  border-top: 1px solid var(--line);
  padding: 32px 0 48px;
}
.foot-in {
  display: flex;
  flex-wrap: wrap;
  align-items: baseline;
  gap: 10px 24px;
  font-size: 13.5px;
  color: var(--ink-3);
}
.foot-in a { transition: color 0.18s ease; }
.foot-in a:hover { color: var(--ink); }
.foot-in .copy { margin-left: auto; }

/* ---------------- 404 ---------------- */
.nf {
  max-width: var(--w);
  margin: 0 auto;
  padding: 120px 28px 140px;
}
.nf-code {
  font-size: 56px;
  font-weight: 600;
  letter-spacing: -0.04em;
  color: var(--line-2);
}
.nf h1 { font-size: 26px; margin: 22px 0 12px; }
.nf p { margin: 0 0 30px; color: var(--ink-2); }

/* ---------------- 移动端 ---------------- */
@media (max-width: 640px) {
  body { font-size: 15.5px; }
  .bar-in { padding: 0 20px; height: 56px; }
  .bar nav { gap: 16px; font-size: 14px; }
  .wrap { padding: 0 20px; }
  main { padding: 48px 0 72px; }
  h1 { font-size: 30px; }
  .lead { margin-top: 18px; font-size: 16px; }
  .block { margin-top: 48px; padding-top: 34px; }
  .demo-line { font-size: 20px; letter-spacing: 0.02em; }
  .nf { padding: 80px 20px 100px; }
  .foot-in .copy { margin-left: 0; }
}

@media (prefers-reduced-motion: reduce) {
  * { transition-duration: 0.01ms !important; }
  html { scroll-behavior: auto; }
}