:root {
  --bg: #0b1220;
  --bg-elev: #121a2b;
  --bg-card: #162033;
  --border: #243049;
  --text: #e8eefc;
  --muted: #9aa8c7;
  --accent: #5b8cff;
  --accent-2: #35d0ba;
  --warn: #f5a524;
  --danger: #ff6b7a;
  --ok: #3dd68c;
  --code-bg: #0a101c;
  --shadow: 0 10px 40px rgba(0,0,0,.35);
  --radius: 14px;
  --font: "Segoe UI", "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", sans-serif;
  --mono: "JetBrains Mono", "Fira Code", Consolas, monospace;
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  font-family: var(--font);
  background: radial-gradient(1200px 600px at 10% -10%, #1a2a4a 0%, transparent 50%),
              radial-gradient(900px 500px at 90% 0%, #14352f 0%, transparent 45%),
              var(--bg);
  color: var(--text);
  line-height: 1.65;
  min-height: 100vh;
}

a { color: var(--accent); text-decoration: none; }
a:hover { text-decoration: underline; }

.topbar {
  position: sticky; top: 0; z-index: 50;
  display: flex; align-items: center; gap: 1rem;
  padding: .75rem 1.25rem;
  background: rgba(11,18,32,.88);
  backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--border);
}
.brand { display: flex; align-items: center; gap: .6rem; color: var(--text); font-weight: 700; }
.brand:hover { text-decoration: none; }
.brand-mark {
  width: 34px; height: 34px; border-radius: 9px;
  display: grid; place-items: center;
  background: linear-gradient(135deg, var(--accent), var(--accent-2));
  color: #061018; font-size: .85rem; font-weight: 800;
}
.topnav { display: flex; gap: 1rem; margin-left: .5rem; }
.topnav a { color: var(--muted); font-size: .95rem; }
.topnav a:hover, .topnav a.active { color: var(--text); }
.search-mini { margin-left: auto; }
.search-mini input {
  width: min(280px, 36vw);
  padding: .5rem .8rem;
  border-radius: 999px;
  border: 1px solid var(--border);
  background: var(--bg-elev);
  color: var(--text);
  outline: none;
}
.search-mini input:focus { border-color: var(--accent); }
.nav-toggle {
  display: none;
  background: var(--bg-card);
  border: 1px solid var(--border);
  color: var(--text);
  border-radius: 8px;
  padding: .35rem .6rem;
  cursor: pointer;
}

.main { max-width: 1100px; margin: 0 auto; padding: 1.5rem 1.25rem 3rem; }
.site-footer {
  text-align: center; color: var(--muted); font-size: .85rem;
  padding: 1.5rem; border-top: 1px solid var(--border);
}

.hero {
  padding: 2.2rem 1.8rem;
  border-radius: calc(var(--radius) + 4px);
  background: linear-gradient(145deg, #1a2742, #12281f 70%);
  border: 1px solid var(--border);
  box-shadow: var(--shadow);
  margin-bottom: 2rem;
}
.hero h1 { margin: 0 0 .6rem; font-size: clamp(1.6rem, 4vw, 2.3rem); line-height: 1.25; }
.hero p { margin: 0; color: var(--muted); max-width: 52ch; }
.hero-actions { margin-top: 1.2rem; display: flex; flex-wrap: wrap; gap: .7rem; }
.btn {
  display: inline-flex; align-items: center; gap: .4rem;
  padding: .55rem 1rem; border-radius: 999px;
  border: 1px solid var(--border);
  background: var(--bg-card); color: var(--text);
  cursor: pointer; font-size: .92rem;
}
.btn:hover { text-decoration: none; border-color: var(--accent); }
.btn-primary {
  background: linear-gradient(135deg, var(--accent), #3a6fe0);
  border-color: transparent; color: #fff; font-weight: 600;
}
.btn-ok { background: rgba(61,214,140,.15); border-color: var(--ok); color: var(--ok); }
.btn-ghost { background: transparent; }

.section-title {
  display: flex; align-items: baseline; justify-content: space-between;
  gap: 1rem; margin: 2rem 0 1rem;
}
.section-title h2 { margin: 0; font-size: 1.25rem; }
.section-title span { color: var(--muted); font-size: .85rem; }

.roadmap {
  display: grid; gap: .8rem;
  grid-template-columns: repeat(4, 1fr);
  margin-bottom: 2rem;
}
.road-stage {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1rem;
  position: relative;
}
.road-stage .stage-tag {
  font-size: .72rem; font-weight: 700; letter-spacing: .04em;
  color: var(--accent-2); text-transform: uppercase;
}
.road-stage h3 { margin: .35rem 0 .5rem; font-size: 1rem; }
.road-stage ul { margin: 0; padding-left: 1.1rem; color: var(--muted); font-size: .86rem; }
.road-stage a { color: var(--text); }
.road-stage.done { border-color: rgba(61,214,140,.45); }

.cat-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(240px, 1fr));
  gap: 1rem;
}
.cat-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.1rem 1.15rem;
  transition: transform .15s ease, border-color .15s;
  display: block; color: inherit;
}
.cat-card:hover { transform: translateY(-2px); border-color: var(--accent); text-decoration: none; }
.cat-card .icon { font-size: 1.4rem; margin-bottom: .4rem; }
.cat-card h3 { margin: 0 0 .35rem; font-size: 1.05rem; }
.cat-card p { margin: 0; color: var(--muted); font-size: .86rem; }
.cat-card .meta {
  margin-top: .75rem; display: flex; justify-content: space-between;
  font-size: .8rem; color: var(--muted);
}
.progress-bar {
  height: 6px; background: var(--bg); border-radius: 99px; overflow: hidden; margin-top: .55rem;
}
.progress-bar > i {
  display: block; height: 100%; background: linear-gradient(90deg, var(--accent), var(--accent-2));
  width: 0%;
}

.lesson-list { display: grid; gap: .65rem; }
.lesson-item {
  display: flex; gap: .9rem; align-items: flex-start;
  padding: 1rem 1.1rem;
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  color: inherit;
}
.lesson-item:hover { border-color: var(--accent); text-decoration: none; }
.lesson-item.done { border-color: rgba(61,214,140,.35); }
.lesson-num {
  flex: 0 0 2rem; height: 2rem; border-radius: 8px;
  display: grid; place-items: center;
  background: var(--bg); color: var(--muted); font-size: .85rem; font-weight: 700;
}
.lesson-item.done .lesson-num { background: rgba(61,214,140,.2); color: var(--ok); }
.lesson-item h3 { margin: 0 0 .25rem; font-size: 1rem; }
.lesson-item p { margin: 0; color: var(--muted); font-size: .85rem; }
.badges { display: flex; flex-wrap: wrap; gap: .4rem; margin-top: .45rem; }
.badge {
  font-size: .72rem; padding: .15rem .45rem; border-radius: 999px;
  border: 1px solid var(--border); color: var(--muted);
}
.badge.diff-入门, .badge.diff-初级 { color: var(--ok); border-color: rgba(61,214,140,.4); }
.badge.diff-中级 { color: var(--warn); border-color: rgba(245,165,36,.4); }
.badge.diff-高级 { color: var(--danger); border-color: rgba(255,107,122,.4); }

.crumb { color: var(--muted); font-size: .85rem; margin-bottom: 1rem; }
.crumb a { color: var(--muted); }
.crumb a:hover { color: var(--text); }

.lesson-layout {
  display: grid;
  grid-template-columns: 1fr 220px;
  gap: 1.5rem;
  align-items: start;
}
.lesson-article {
  background: var(--bg-elev);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.4rem 1.5rem 2rem;
}
.lesson-article h1 { margin: 0 0 .6rem; font-size: 1.55rem; line-height: 1.3; }
.lesson-meta { display: flex; flex-wrap: wrap; gap: .5rem; margin-bottom: 1rem; }
.objectives {
  background: rgba(91,140,255,.08);
  border: 1px solid rgba(91,140,255,.25);
  border-radius: 12px;
  padding: .9rem 1rem;
  margin: 1rem 0 1.4rem;
}
.objectives h3 { margin: 0 0 .4rem; font-size: .95rem; color: var(--accent); }
.objectives ul { margin: 0; padding-left: 1.2rem; }
.lesson-body h2 {
  margin: 1.6rem 0 .7rem; font-size: 1.2rem;
  padding-bottom: .35rem; border-bottom: 1px solid var(--border);
}
.lesson-body h3 { margin: 1.2rem 0 .5rem; font-size: 1.05rem; }
.lesson-body p, .lesson-body li { color: #d5dff3; }
.lesson-body ul, .lesson-body ol { padding-left: 1.25rem; }
.lesson-body code {
  font-family: var(--mono); font-size: .88em;
  background: var(--code-bg); padding: .1rem .35rem; border-radius: 4px;
}
.lesson-body pre {
  background: var(--code-bg);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 1rem;
  overflow-x: auto;
  font-family: var(--mono);
  font-size: .84rem;
  line-height: 1.55;
}
.lesson-body pre code { background: none; padding: 0; }
.callout {
  border-radius: 12px; padding: .9rem 1rem; margin: 1rem 0;
  border: 1px solid var(--border); background: var(--bg-card);
}
.callout.pitfall { border-color: rgba(255,107,122,.35); background: rgba(255,107,122,.08); }
.callout.when { border-color: rgba(53,208,186,.35); background: rgba(53,208,186,.08); }
.callout.interview { border-color: rgba(245,165,36,.4); background: rgba(245,165,36,.08); }
.callout h3 { margin: 0 0 .4rem; font-size: .95rem; }
.lesson-nav {
  display: flex; justify-content: space-between; gap: .8rem;
  margin-top: 1.5rem; flex-wrap: wrap;
}
.toc-side {
  position: sticky; top: 72px;
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1rem;
}
.toc-side h4 { margin: 0 0 .6rem; font-size: .85rem; color: var(--muted); }
.toc-side a {
  display: block; color: var(--muted); font-size: .82rem;
  padding: .25rem 0; border-left: 2px solid transparent; padding-left: .55rem;
}
.toc-side a:hover { color: var(--text); border-left-color: var(--accent); text-decoration: none; }

.search-page input {
  width: 100%; padding: .85rem 1rem; font-size: 1rem;
  border-radius: 12px; border: 1px solid var(--border);
  background: var(--bg-card); color: var(--text); outline: none;
}
.search-page input:focus { border-color: var(--accent); }
.search-results { margin-top: 1rem; display: grid; gap: .6rem; }
.search-hit {
  display: block; padding: .9rem 1rem;
  background: var(--bg-card); border: 1px solid var(--border);
  border-radius: var(--radius); color: inherit;
}
.search-hit:hover { border-color: var(--accent); text-decoration: none; }
.search-hit .cat { color: var(--accent-2); font-size: .75rem; }
.mark { background: rgba(245,165,36,.35); color: inherit; border-radius: 2px; padding: 0 2px; }

.stats-row {
  display: grid; grid-template-columns: repeat(3, 1fr); gap: .8rem; margin-bottom: 1.5rem;
}
.stat {
  background: var(--bg-card); border: 1px solid var(--border);
  border-radius: var(--radius); padding: 1rem; text-align: center;
}
.stat strong { display: block; font-size: 1.5rem; color: var(--accent-2); }
.stat span { color: var(--muted); font-size: .85rem; }

.empty { color: var(--muted); padding: 2rem; text-align: center; }

@media (max-width: 860px) {
  .roadmap { grid-template-columns: 1fr 1fr; }
  .lesson-layout { grid-template-columns: 1fr; }
  .toc-side { position: static; order: -1; }
  .nav-toggle { display: inline-block; margin-left: auto; }
  .topnav {
    display: none; position: absolute; top: 58px; left: 0; right: 0;
    flex-direction: column; background: var(--bg-elev);
    border-bottom: 1px solid var(--border); padding: .8rem 1.25rem;
  }
  .topnav.open { display: flex; }
  .search-mini { display: none; }
  .stats-row { grid-template-columns: 1fr; }
}
@media (max-width: 520px) {
  .roadmap { grid-template-columns: 1fr; }
}