:root {
  --bg: #F4F7FD;
  --panel: #FFFFFF;
  --panel-2: #ECF1F9;
  --border: #D9E1EE;
  --border-strong: #C5D0E0;
  --accent: #1F6BD1;
  --accent-dark: #154E9E;
  --accent-soft: #E7EFFB;
  --text: #1E2A36;
  --muted: #5A6675;
  --success: #2E9E5B;
  --warn: #C98A00;
  --error: #D2423A;
  --marker: #FFE36A;
  --on-accent: #FFFFFF;
  --chrome-dot: #C9D2DE;
  --toggle-off: #CBD4E1;
  --log-bg: #1B2631;
  --log-text: #D3DCE8;
  --log-dim: #8796A8;
  --shadow-soft: rgba(30, 42, 54, 0.06);
  --shadow-deep: rgba(30, 42, 54, 0.11);
  --accent-glow: rgba(31, 107, 209, 0.30);
  --grid-line: rgba(90, 102, 117, 0.10);
  --mask-solid: #000000;
  --clear: transparent;
  --font-display: "Inter", "Noto Sans SC", "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", system-ui, sans-serif;
  --font-body: "Inter", "Noto Sans SC", "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", system-ui, sans-serif;
  --font-mono: "JetBrains Mono", ui-monospace, "SFMono-Regular", Menlo, Consolas, monospace;
  --r-ctl: 4px;
  --r-card: 6px;
  --r-panel: 8px;
  --r-knob: 2px;
  --r-round: 50%;
  --header-h: 72px;
  --gutter: 48px;
  --wrap-max: 1440px;
  --reading-max: 840px;
  --weight-body: 400;
  --weight-medium: 500;
  --weight-semibold: 600;
  --weight-bold: 700;
  --weight-heavy: 800;
  --weight-display: 900;
  --size-body: 16px;
  --size-small: 14px;
  --size-h1: clamp(34px, 3.4vw, 48px);
  --size-h2: clamp(22px, 2.1vw, 30px);
  --size-h3: 22px;
  --space-section: 80px;
  --shadow-card: 0 1px 2px var(--shadow-soft), 0 18px 48px -22px var(--shadow-deep);
  --ease-short: 150ms ease;
  --ease-reveal: 500ms ease;
}
*, *::before, *::after { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; scroll-behavior: smooth; scroll-padding-top: 24px; }
html.nav-open { overflow: hidden; }
body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: var(--font-body);
  font-size: var(--size-body);
  font-weight: var(--weight-body);
  line-height: 1.7;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}
img, svg { max-width: 100%; vertical-align: middle; }
img { height: auto; }
button, input, select, textarea { font: inherit; }
button { cursor: pointer; }
button, a, summary { -webkit-tap-highlight-color: var(--clear); }
a { color: var(--accent); text-underline-offset: 4px; }
a:hover { color: var(--accent-dark); }
:focus-visible { outline: 2px solid var(--accent); outline-offset: 3px; border-radius: var(--r-ctl); }
[hidden] { display: none !important; }
h1, h2, h3 {
  font-family: var(--font-display);
  font-weight: var(--weight-display);
  line-height: 1.25;
  letter-spacing: -0.012em;
  text-wrap: balance;
  overflow-wrap: break-word;
}
h1 { font-size: var(--size-h1); line-height: 1.12; }
h2 { font-size: var(--size-h2); }
h3 { font-size: var(--size-h3); }
p { margin: 0 0 1em; }
strong, b { font-weight: var(--weight-bold); }
code, pre, kbd, samp { font-family: var(--font-mono); }
code { overflow-wrap: anywhere; word-break: normal; }
pre {
  max-width: 100%;
  min-width: 0;
  overflow-x: auto;
  padding: 20px;
  border: 1px solid var(--border);
  border-radius: var(--r-card);
  background: var(--panel-2);
  color: var(--text);
  line-height: 1.7;
  tab-size: 2;
}
pre code { white-space: pre; overflow-wrap: normal; word-break: normal; }
blockquote { margin-inline: 0; }
hr { border: 0; border-top: 1px solid var(--border); }
.wrap {
  width: 100%;
  max-width: var(--wrap-max);
  margin-inline: auto;
  padding-inline: var(--gutter);
}
.reading { max-width: var(--reading-max); margin-inline: auto; min-width: 0; }
.section { padding-top: var(--space-section); padding-bottom: var(--space-section); }
.section-title { margin-top: 0; margin-bottom: 28px; }
.prose { min-width: 0; line-height: 1.9; }
.prose h2 { margin-top: 2.2em; margin-bottom: 0.8em; }
.prose h3 { margin-top: 1.7em; }
.prose p, .prose li { overflow-wrap: break-word; }
.prose > :first-child { margin-top: 0; }
.prose img { max-width: 100%; }
.prose div, .prose section, .prose article { min-width: 0; max-width: 100%; }
.muted { color: var(--muted); }
.mono { font-family: var(--font-mono); }
.no-break { white-space: nowrap; }
.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip-path: inset(50%);
  white-space: nowrap;
  border: 0;
}
.skip-link { position: fixed; top: 8px; left: var(--gutter); z-index: 100; transform: translateY(-160%); }
.skip-link:focus { transform: none; }
.grid { display: grid; gap: 24px; }
.grid > *, .letter > *, .hero-grid > *, .footer-grid > * { min-width: 0; }
.grid-two { grid-template-columns: repeat(2, minmax(0, 1fr)); }
.card, .panel {
  min-width: 0;
  padding: 28px;
  border: 1px solid var(--border);
  background: var(--panel);
  color: var(--text);
  box-shadow: var(--shadow-card);
}
.card { border-radius: var(--r-card); }
.panel { border-radius: var(--r-panel); }
.card h3, .panel h3 { margin-top: 0; }
.mk {
  background-image: linear-gradient(to top, var(--marker) 0, var(--marker) 40%, var(--clear) 40%);
  padding: 0 0.1em;
  margin: 0 -0.04em;
  -webkit-box-decoration-break: clone;
  box-decoration-break: clone;
}
.cta-row { margin-top: 28px; display: flex; flex-wrap: wrap; gap: 12px; }
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 9px;
  min-height: 48px;
  padding: 0 22px;
  border: 1px solid var(--clear);
  border-radius: var(--r-ctl);
  font-family: var(--font-body);
  font-size: var(--size-body);
  font-weight: var(--weight-bold);
  line-height: 1.4;
  text-decoration: none;
  text-align: center;
  transition: transform var(--ease-short), background-color var(--ease-short);
}
.btn svg, .icon {
  width: 18px;
  height: 18px;
  flex-shrink: 0;
  fill: none;
  stroke: currentColor;
  stroke-width: 2;
  stroke-linecap: round;
  stroke-linejoin: round;
}
.btn:hover { transform: translateY(-1px); }
.btn-primary {
  background: var(--accent);
  color: var(--on-accent);
  box-shadow: 0 1px 0 var(--accent-dark), 0 10px 22px -10px var(--accent-glow);
}
.btn-primary:hover, .btn-primary.is-hover { background: var(--accent-dark); color: var(--on-accent); }
.btn-ghost {
  background: var(--panel);
  color: var(--text);
  border-color: var(--border);
  box-shadow: 0 1px 2px var(--shadow-soft);
}
.btn-ghost:hover, .btn-ghost.is-hover { border-color: var(--accent); color: var(--accent-dark); }
.btn:active, .btn.is-active { transform: translateY(1px); }
.btn:disabled, .btn[aria-disabled="true"] {
  cursor: not-allowed;
  background: var(--panel-2);
  color: var(--muted);
  border-color: var(--border);
  box-shadow: none;
  transform: none;
}
.btn.is-focus { outline: 2px solid var(--accent); outline-offset: 3px; }

.topbar, #site-header { position: relative; z-index: 60; }
.topbar-in {
  max-width: min(100%, calc(1280px + var(--gutter) * 2));
  margin-inline: auto;
  padding-inline: var(--gutter);
  height: var(--header-h);
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 32px;
}
.brand {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  color: var(--text);
  text-decoration: none;
  flex-shrink: 0;
}
.brand:hover { color: var(--text); }
.brand-mark { width: 32px; height: 32px; flex-shrink: 0; border-radius: var(--r-card); }
.brand-name {
  font-family: var(--font-display);
  font-weight: var(--weight-display);
  font-size: 18px;
  letter-spacing: -0.005em;
}
.nav { display: flex; align-items: center; gap: 32px; min-width: 0; margin-left: auto; }
.nav ul {
  display: flex;
  align-items: center;
  list-style: none;
  margin: 0;
  padding: 0;
  gap: 30px;
}
.nav ul a {
  display: block;
  color: var(--muted);
  text-decoration: none;
  font-size: 15px;
  font-weight: var(--weight-medium);
  white-space: nowrap;
}
.nav ul a:hover { color: var(--text); }
.nav a[aria-current="page"] { color: var(--text); font-weight: var(--weight-heavy); }
.header-tools { display: flex; align-items: center; gap: 10px; flex-shrink: 0; }
.lang { position: relative; flex-shrink: 0; }
.lang-button, .lang summary {
  display: block;
  list-style: none;
  cursor: pointer;
  font-size: var(--size-small);
  font-weight: var(--weight-semibold);
  color: var(--text);
  padding: 6px 12px;
  border: 1px solid var(--border);
  border-radius: var(--r-ctl);
  background: var(--panel);
  white-space: nowrap;
}
.lang summary::-webkit-details-marker { display: none; }
.lang-list, .lang > ul {
  position: absolute;
  right: 0;
  top: calc(100% + 6px);
  list-style: none;
  margin: 0;
  padding: 6px;
  min-width: 160px;
  background: var(--panel);
  color: var(--text);
  border: 1px solid var(--border);
  border-radius: var(--r-card);
  box-shadow: 0 16px 40px -12px var(--shadow-deep);
  z-index: 4;
}
.lang-list a, .lang > ul a {
  display: flex;
  align-items: center;
  min-height: 44px;
  padding: 6px 10px;
  border-radius: var(--r-ctl);
  font-size: var(--size-small);
  color: var(--text);
  text-decoration: none;
}
.lang-list a:hover, .lang > ul a:hover { background: var(--panel-2); color: var(--text); }
.menu-button {
  display: none;
  align-items: center;
  justify-content: center;
  min-width: 44px;
  min-height: 44px;
  border: 1px solid var(--border);
  border-radius: var(--r-ctl);
  background: var(--panel);
  color: var(--text);
}
.menu-button svg { width: 22px; height: 22px; flex-shrink: 0; fill: none; stroke: currentColor; stroke-width: 2; }
.mobile-nav { display: none; }
.footer { padding-top: 56px; padding-bottom: 96px; border-top: 1px solid var(--border); }
.footer-grid { display: grid; grid-template-columns: 1.2fr 0.8fr 1.2fr 0.8fr; gap: 36px; }
.footer h2 { font-size: 16px; margin-top: 0; margin-bottom: 16px; font-weight: var(--weight-heavy); }
.footer p { margin-top: 18px; color: var(--muted); font-size: var(--size-small); }
.footer ul { list-style: none; padding: 0; margin: 0; }
.footer li { margin-bottom: 8px; }
.footer li a { font-size: var(--size-small); text-decoration: none; }
.footer-bottom { margin-top: 36px; padding-top: 20px; border-top: 1px solid var(--border); color: var(--muted); font-size: var(--size-small); }
.letter { display: grid; grid-template-columns: minmax(0, 3fr) minmax(0, 7fr); gap: 56px; align-items: start; }
.letter > h2 { position: sticky; top: 24px; margin: 0; }
.letter p { margin: 0 0 16px; font-size: 17px; line-height: 1.9; color: var(--muted); }
.letter p a { font-weight: var(--weight-bold); }
.reveal { opacity: 1; transform: none; }
.reveal-ready .reveal { opacity: 0; transform: translateY(12px); transition: opacity var(--ease-reveal), transform var(--ease-reveal); }
.reveal-ready .reveal.shown { opacity: 1; transform: none; }
.decorated, .hero { position: relative; overflow-x: clip; }

@media (max-width: 1279px) {
  .nav { display: none; }
  .header-tools { margin-left: auto; }
  .menu-button { display: inline-flex; }
  .mobile-nav:not([hidden]) {
    display: block;
    position: absolute;
    top: 100%;
    left: 0;
    right: 0;
    z-index: 3;
    max-height: calc(100dvh - var(--header-h));
    overflow-y: auto;
    overscroll-behavior: contain;
    padding: 16px var(--gutter) 24px;
    border-top: 1px solid var(--border);
    border-bottom: 1px solid var(--border);
    background: var(--panel);
    color: var(--text);
    box-shadow: 0 24px 40px -20px var(--shadow-deep);
  }
  .mobile-nav ul { list-style: none; margin: 0; padding: 0; }
  .mobile-nav a { display: flex; align-items: center; width: 100%; min-height: 44px; padding: 10px 12px; color: var(--text); text-decoration: none; border-radius: var(--r-ctl); }
  .mobile-nav a:hover { background: var(--panel-2); color: var(--accent-dark); }
  .mobile-nav a[aria-current] { font-weight: var(--weight-heavy); color: var(--accent-dark); }
  .mobile-languages { margin-top: 16px; padding-top: 16px; border-top: 1px solid var(--border); }
  .mobile-languages p { margin: 0 12px 8px; color: var(--muted); font-size: var(--size-small); }
}
@media (max-width: 1180px) { :root { --gutter: 32px; } }
@media (max-width: 960px) {
  .grid-two { grid-template-columns: minmax(0, 1fr); }
  .letter { grid-template-columns: minmax(0, 1fr); gap: 16px; }
  .letter > h2 { position: static; }
  .footer-grid { grid-template-columns: repeat(2, minmax(0, 1fr)); }
}
@media (max-width: 768px) {
  :root { --size-h1: clamp(24px, 5vw, 30px); --space-section: 48px; }
}
@media (max-width: 640px) {
  :root { --gutter: 18px; }
  .tilt, [data-tilt] { transform: none !important; }
  .topbar-in { gap: 12px; }
  .brand-name { font-size: 15px; }
  .brand { gap: 8px; }
  .header-tools { gap: 6px; margin-left: auto; }
  .lang-button, .lang summary { padding-inline: 8px; font-size: 12px; }
  .card, .panel { padding: 20px; }
}
@media (max-width: 400px) {
  .topbar-in .brand-name { font-size: 13px; }
  .topbar-in .brand-mark { width: 26px; height: 26px; }
  .footer-grid { grid-template-columns: minmax(0, 1fr); gap: 28px; }
}
@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  *, *::before, *::after { animation: none !important; transition: none !important; }
  .reveal-ready .reveal { opacity: 1; transform: none; }
  .btn:hover { transform: none; }
}