:root {
  --ustc-blue: #a6caec;
  --ustc-blue-deep: #344354;
  --ustc-blue-ink: #303943;
  --blue-surface: #e3f3fc;
  --blue-surface-strong: #a6caec;
  --sky: #a6caec;
  --sky-soft: #e3f3fc;
  --gray: #bfbfbf;
  --gray-soft: #f3f4f5;
  --ink: #303943;
  --muted: #5d6a74;
  --paper: #ffffff;
  --white: #ffffff;
  --orange: #f28c28;
  --orange-deep: #c86612;
  --border: #bfbfbf;
  --shadow: 0 20px 50px rgba(166, 202, 236, 0.18);
  --radius-sm: 10px;
  --radius-md: 18px;
  --radius-lg: 28px;
  --content: 1120px;
  --reading: 760px;
  --font-sans: Georgia, "Times New Roman", "Songti SC", SimSun, serif;
  --font-display: Georgia, "Times New Roman", "Songti SC", SimSun, serif;
  --font-mono: Georgia, "Times New Roman", "Songti SC", SimSun, serif;
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; scroll-padding-top: 92px; }
body {
  margin: 0;
  color: var(--ink);
  background: var(--paper);
  font-family: var(--font-sans);
  font-size: 17px;
  line-height: 1.72;
  -webkit-font-smoothing: antialiased;
}
img { display: block; max-width: 100%; }
a { color: inherit; }
button { font: inherit; }
::selection { color: var(--ustc-blue-deep); background: var(--sky); }

.section-shell { width: min(calc(100% - 40px), var(--content)); margin-inline: auto; }
.skip-link { position: fixed; left: 16px; top: -80px; z-index: 999; padding: 10px 14px; background: var(--orange); color: var(--ink); border-radius: 8px; font-weight: 700; }
.skip-link:focus { top: 12px; }
.kicker, .eyebrow { margin: 0; font-family: var(--font-mono); font-size: .78rem; font-weight: 500; letter-spacing: .13em; text-transform: uppercase; color: var(--orange-deep); }
h1, h2, h3, p { text-wrap: pretty; }
h1, h2 { font-family: var(--font-display); }
h2 { margin: 0; color: var(--ustc-blue-deep); font-size: clamp(2.2rem, 5vw, 4rem); line-height: 1; letter-spacing: -.03em; }

@media (max-width: 720px) {
  body { font-size: 16px; }
  .section-shell { width: min(calc(100% - 28px), var(--content)); }
}

@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  *, *::before, *::after { animation-duration: .01ms !important; animation-iteration-count: 1 !important; transition-duration: .01ms !important; }
}