:root {
  --bg: #f6f7fb;
  --card: #ffffff;
  --ink: #1d2333;
  --muted: #5c6577;
  --line: #e4e7f0;
  --brand: #4f46e5;
  --brand-soft: #eef0fe;
  --teal: #0d9488;
  --teal-soft: #e6f7f4;
  --amber: #b45309;
  --amber-soft: #fdf3e3;
  --rose: #be123c;
  --rose-soft: #fdeef2;
  --radius: 14px;
  --shadow: 0 1px 3px rgba(28, 35, 51, 0.07), 0 8px 24px rgba(28, 35, 51, 0.05);
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  font-family: -apple-system, BlinkMacSystemFont, "PingFang SC", "Hiragino Sans GB",
    "Microsoft YaHei", "Noto Sans SC", "Segoe UI", sans-serif;
  color: var(--ink);
  background: var(--bg);
  line-height: 1.7;
}

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

.container { max-width: 1100px; margin: 0 auto; padding: 0 20px; }

/* ---------- Top navigation ---------- */
.topbar {
  position: sticky; top: 0; z-index: 50;
  background: rgba(255, 255, 255, 0.92);
  backdrop-filter: blur(8px);
  border-bottom: 1px solid var(--line);
}
.nav-inner {
  max-width: 1100px; margin: 0 auto; padding: 0 20px;
  display: flex; align-items: center; justify-content: space-between; gap: 16px;
  height: 60px;
}
.logo { font-weight: 800; font-size: 17px; letter-spacing: 0.2px; color: var(--ink); }
.logo .dot { color: var(--teal); }
.nav-links { display: flex; gap: 6px; align-items: center; flex-wrap: wrap; }
.nav-links a {
  padding: 7px 12px; border-radius: 999px; color: var(--muted); font-size: 14.5px; font-weight: 500;
}
.nav-links a:hover { background: var(--brand-soft); color: var(--brand); text-decoration: none; }
.nav-links a.active { background: var(--brand); color: #fff; }
.nav-toggle { display: none; background: none; border: 1px solid var(--line); border-radius: 8px; padding: 6px 10px; cursor: pointer; font-size: 18px; }

@media (max-width: 760px) {
  .nav-toggle { display: block; }
  .nav-links {
    display: none; position: absolute; top: 60px; left: 0; right: 0;
    background: #fff; border-bottom: 1px solid var(--line); padding: 10px 20px 16px;
    flex-direction: column; align-items: stretch;
  }
  .nav-links.open { display: flex; }
  .nav-links a { padding: 10px 12px; border-radius: 8px; }
}

/* ---------- Hero ---------- */
.hero {
  padding: 64px 0 56px;
  background:
    radial-gradient(1000px 320px at 85% -10%, rgba(79, 70, 229, 0.12), transparent 60%),
    radial-gradient(800px 300px at 10% 0%, rgba(13, 148, 136, 0.10), transparent 60%);
}
.hero h1 { font-size: clamp(30px, 4.6vw, 46px); line-height: 1.2; margin: 0 0 14px; letter-spacing: -0.5px; }
.hero .sub { font-size: clamp(16px, 2vw, 19px); color: var(--muted); max-width: 720px; margin: 0 0 22px; }
.hero-badges { display: flex; gap: 10px; flex-wrap: wrap; margin-bottom: 8px; }

.badge {
  display: inline-block; padding: 3px 11px; border-radius: 999px;
  font-size: 13px; font-weight: 600; background: var(--brand-soft); color: var(--brand);
}
.badge.teal { background: var(--teal-soft); color: var(--teal); }
.badge.amber { background: var(--amber-soft); color: var(--amber); }
.badge.rose { background: var(--rose-soft); color: var(--rose); }
.badge.gray { background: #eef0f4; color: var(--muted); }

/* ---------- Sections ---------- */
section { padding: 44px 0; }
.section-title { font-size: 26px; margin: 0 0 6px; letter-spacing: -0.3px; }
.section-desc { color: var(--muted); margin: 0 0 24px; max-width: 780px; }

.card {
  background: var(--card); border: 1px solid var(--line); border-radius: var(--radius);
  padding: 20px 22px; box-shadow: var(--shadow);
}
.cards-grid {
  display: grid; grid-template-columns: repeat(auto-fill, minmax(290px, 1fr)); gap: 16px;
}
.cards-grid .card { margin: 0; }
.card h3 { margin: 0 0 8px; font-size: 17px; }
.card p { margin: 6px 0; color: var(--muted); font-size: 14.5px; }
.card .card-meta { font-size: 13px; color: var(--muted); margin-bottom: 8px; }
.card ul { margin: 8px 0 0; padding-left: 18px; color: var(--muted); font-size: 14.5px; }
.card li { margin: 3px 0; }

.nav-cards .card { cursor: pointer; transition: transform 0.15s ease, box-shadow 0.15s ease; }
.nav-cards .card:hover { transform: translateY(-3px); box-shadow: 0 10px 28px rgba(28, 35, 51, 0.10); }
.nav-cards .card h3 { color: var(--brand); }

/* ---------- Roadmap / timeline ---------- */
.timeline { list-style: none; margin: 0; padding: 0; }
.timeline > li { position: relative; padding: 0 0 26px 34px; }
.timeline > li::before {
  content: ""; position: absolute; left: 9px; top: 22px; bottom: -4px; width: 2px; background: var(--line);
}
.timeline > li:last-child::before { display: none; }
.timeline .dot {
  position: absolute; left: 0; top: 4px; width: 20px; height: 20px; border-radius: 50%;
  background: var(--brand); color: #fff; font-size: 11px; display: flex; align-items: center; justify-content: center;
}
.timeline .dot.teal { background: var(--teal); }
.timeline .dot.amber { background: var(--amber); }
.timeline .dot.rose { background: var(--rose); }
.stage-head { display: flex; align-items: baseline; gap: 10px; flex-wrap: wrap; }
.stage-head h3 { margin: 0; font-size: 18px; }
.stage-head .time { color: var(--muted); font-size: 13.5px; }
.stage-body { margin-top: 10px; }
.stage-body .task { display: flex; align-items: flex-start; gap: 10px; margin: 7px 0; color: var(--muted); font-size: 14.8px; }
.stage-body .task input { margin-top: 5px; accent-color: var(--brand); }
.stage-body .task.done span { text-decoration: line-through; color: #9aa2b2; }
.stage-note { margin-top: 10px; font-size: 13.5px; color: var(--muted); background: var(--brand-soft); border-radius: 10px; padding: 8px 12px; }

.progress-wrap { margin: 18px 0 4px; }
.progress-label { font-size: 13.5px; color: var(--muted); margin-bottom: 6px; }
.progress-bar { height: 8px; background: #e9ebf3; border-radius: 999px; overflow: hidden; }
.progress-fill { height: 100%; width: 0; background: linear-gradient(90deg, var(--brand), var(--teal)); transition: width 0.3s ease; }

/* ---------- Filters ---------- */
.filters { display: flex; gap: 8px; flex-wrap: wrap; margin: 0 0 18px; }
.chip {
  border: 1px solid var(--line); background: #fff; color: var(--muted);
  border-radius: 999px; padding: 6px 14px; font-size: 13.5px; font-weight: 600; cursor: pointer;
}
.chip:hover { border-color: var(--brand); color: var(--brand); }
.chip.active { background: var(--brand); border-color: var(--brand); color: #fff; }

.searchbox {
  width: 100%; max-width: 420px; padding: 10px 14px; border: 1px solid var(--line);
  border-radius: 10px; font-size: 14.5px; margin: 0 0 18px; background: #fff; color: var(--ink);
}
.searchbox:focus { outline: 2px solid var(--brand-soft); border-color: var(--brand); }

/* ---------- Tables ---------- */
.table-wrap { overflow-x: auto; background: #fff; border: 1px solid var(--line); border-radius: var(--radius); box-shadow: var(--shadow); }
table { width: 100%; border-collapse: collapse; font-size: 14px; min-width: 640px; }
th { text-align: left; padding: 12px 16px; background: #fafbff; border-bottom: 1px solid var(--line); font-size: 13px; color: var(--muted); }
td { padding: 12px 16px; border-bottom: 1px solid var(--line); vertical-align: top; }
tr:last-child td { border-bottom: none; }
tr:hover td { background: #fafbff; }

/* ---------- Notes / callouts ---------- */
.note { border-radius: 12px; padding: 14px 18px; margin: 18px 0; font-size: 14.5px; }
.note.tip { background: var(--teal-soft); color: #0f4f48; }
.note.info { background: var(--brand-soft); color: #3b3a9e; }
.note.warn { background: var(--amber-soft); color: #7c4a03; }
.note strong { display: block; margin-bottom: 4px; }

/* ---------- Concepts ---------- */
.concept-group { margin-bottom: 40px; }
.concept-group > h2 { font-size: 22px; margin: 0 0 4px; }
.concept-group > p { color: var(--muted); margin: 0 0 18px; }
.concept { margin-bottom: 16px; }
.concept summary { cursor: pointer; font-weight: 700; font-size: 16px; padding: 2px 0; }
.concept summary:hover { color: var(--brand); }
.concept .one-liner { color: var(--muted); font-size: 14.5px; margin: 6px 0 10px; }
.concept .detail { border-top: 1px dashed var(--line); padding-top: 12px; margin-top: 8px; }
.concept .detail p { margin: 8px 0; font-size: 14.6px; }
.concept .detail ul { margin: 8px 0; padding-left: 20px; color: var(--muted); font-size: 14.4px; }
.concept .related { display: flex; gap: 6px; flex-wrap: wrap; margin-top: 12px; }
.mini-chip {
  font-size: 12.5px; padding: 2px 10px; border-radius: 999px; background: #f1f2f8; color: var(--muted);
}
.mini-chip a { color: inherit; }

/* ---------- Software / tool cards ---------- */
.tool-card { display: flex; flex-direction: column; gap: 8px; }
.tool-card .links { margin-top: auto; display: flex; gap: 8px; flex-wrap: wrap; padding-top: 10px; }
.tool-card .links a { font-size: 13.5px; font-weight: 600; }
.tool-card.hidden, .concept.hidden, .lit-card.hidden { display: none; }

/* ---------- Literature ---------- */
.lit-card { margin-bottom: 14px; }
.lit-card h3 { margin: 0 0 4px; font-size: 16px; }
.lit-card .cite { font-size: 13.5px; color: var(--muted); margin: 0 0 8px; }
.lit-card .why { font-size: 14.3px; color: var(--ink); background: #fafbff; border-left: 3px solid var(--brand); padding: 8px 12px; border-radius: 0 8px 8px 0; margin: 8px 0; }
.lit-card p { margin: 6px 0; font-size: 14.4px; color: var(--muted); }

/* ---------- Glossary ---------- */
.glossary-list { display: grid; grid-template-columns: repeat(auto-fill, minmax(300px, 1fr)); gap: 12px; }
.glossary-list .term { background: #fff; border: 1px solid var(--line); border-radius: 12px; padding: 14px 16px; }
.glossary-list .term.hidden { display: none; }
.glossary-list h3 { margin: 0 0 4px; font-size: 15.5px; }
.glossary-list .en { color: var(--teal); font-weight: 600; font-size: 13.5px; }
.glossary-list p { margin: 6px 0 0; color: var(--muted); font-size: 14px; }

/* ---------- Footer ---------- */
footer {
  border-top: 1px solid var(--line); margin-top: 40px;
  padding: 28px 0 44px; color: var(--muted); font-size: 13.5px;
  background: #fff;
}
footer .container { display: flex; justify-content: space-between; gap: 12px; flex-wrap: wrap; }

/* ---------- Misc ---------- */
.btn {
  display: inline-block; background: var(--brand); color: #fff; padding: 10px 18px;
  border-radius: 10px; font-weight: 700; font-size: 14.5px;
}
.btn:hover { background: #4338ca; text-decoration: none; }
.btn.ghost { background: #fff; color: var(--brand); border: 1px solid var(--line); }
.btn.ghost:hover { border-color: var(--brand); }
.hero-cta { display: flex; gap: 12px; flex-wrap: wrap; margin-top: 8px; }
.back-top {
  position: fixed; right: 22px; bottom: 22px; width: 42px; height: 42px; border-radius: 50%;
  background: var(--brand); color: #fff; border: none; font-size: 18px; cursor: pointer;
  box-shadow: var(--shadow); display: none; z-index: 40;
}
.back-top.show { display: block; }
.kbd { background: #f1f2f8; border-radius: 5px; padding: 1px 6px; font-size: 12.5px; font-family: ui-monospace, SFMono-Regular, Menlo, monospace; }
hr { border: none; border-top: 1px solid var(--line); margin: 28px 0; }

/* ========== Practice mode (companion runbook) ========== */
.practice-hero { padding: 40px 0 28px; }
.practice-hero h1 { font-size: 30px; margin: 0 0 8px; }
.practice-hero .sub { color: var(--muted); margin: 0 0 14px; }

.task-card { display: flex; flex-direction: column; gap: 10px; }
.task-card h3 { margin: 0; font-size: 18px; }
.task-card .meta { display: flex; gap: 8px; flex-wrap: wrap; }
.task-card p { color: var(--muted); font-size: 14.5px; margin: 0; }
.task-card .go { margin-top: auto; }

.progress-wrap.practice { margin: 4px 0 22px; }

.steps { max-width: 720px; margin: 0 auto; }
.step-card {
  background: #fff; border: 1px solid var(--line); border-radius: 16px;
  padding: 22px 20px; margin: 0 0 14px; box-shadow: var(--shadow);
  scroll-margin-top: 90px;
}
.step-head { display: flex; align-items: flex-start; gap: 12px; margin-bottom: 10px; }
.step-num {
  flex: 0 0 34px; height: 34px; border-radius: 50%;
  background: var(--brand); color: #fff; font-weight: 800; font-size: 15px;
  display: flex; align-items: center; justify-content: center;
}
.step-card.done .step-num { background: var(--teal); }
.step-title { margin: 0; font-size: 18px; line-height: 1.35; }
.step-meta { display: flex; gap: 8px; flex-wrap: wrap; margin: 2px 0 12px; }
.step-body { color: var(--ink); font-size: 15px; }
.step-body p { margin: 8px 0; }
.step-body ol, .step-body ul { margin: 8px 0; padding-left: 20px; }
.step-body li { margin: 4px 0; }

.expect {
  background: var(--teal-soft); border-left: 3px solid var(--teal);
  border-radius: 0 10px 10px 0; padding: 10px 14px; margin: 12px 0; font-size: 14.5px;
}
.expect strong { color: #0f4f48; }
.errors { margin: 12px 0 0; }
.errors summary { cursor: pointer; font-weight: 700; font-size: 14.5px; color: var(--amber); }
.errors ul { margin: 8px 0 0; padding-left: 20px; font-size: 14.3px; color: var(--muted); }
.errors li { margin: 5px 0; }

.link-box {
  display: flex; align-items: center; gap: 12px; flex-wrap: wrap;
  background: #fafbff; border: 1px dashed var(--line); border-radius: 12px; padding: 12px 14px; margin-top: 14px;
}
.link-box .url { font-size: 12.5px; color: var(--muted); word-break: break-all; flex: 1 1 160px; }
.link-box canvas { width: 96px; height: 96px; border-radius: 8px; background: #fff; padding: 4px; }
.btn.small { padding: 8px 14px; font-size: 13.5px; border-radius: 9px; }

.step-nav { display: flex; gap: 10px; margin: 20px 0 30px; }
.step-nav .btn { flex: 1; text-align: center; padding: 14px 10px; font-size: 15.5px; }
.step-nav .btn:disabled { opacity: 0.4; cursor: not-allowed; }

.done-banner {
  display: none; background: linear-gradient(90deg, var(--teal), var(--brand));
  color: #fff; border-radius: 14px; padding: 18px 20px; margin: 10px 0 20px; text-align: center;
}
.done-banner.show { display: block; }
.done-banner h3 { margin: 0 0 4px; }

.pay-grid { display: flex; gap: 24px; flex-wrap: wrap; margin: 16px 0; }
.pay-item { text-align: center; }
.pay-item img {
  width: 200px; max-width: 100%; height: auto; max-height: 360px;
  border: 1px solid var(--line); border-radius: 14px; background: #fff; padding: 6px;
}
.pay-item .ph {
  width: 190px; height: 190px; border: 1px dashed var(--line); border-radius: 14px;
  display: flex; align-items: center; justify-content: center;
  color: var(--muted); font-size: 13.5px; background: #fafbff;
}
.pay-item p { margin: 8px 0 0; font-weight: 600; font-size: 14px; color: var(--ink); }

.task-cta { text-align: center; margin: 30px 0 10px; }

/* ---------- Course content pages ---------- */
.lesson { background: #fff; border: 1px solid var(--line); border-radius: 14px; padding: 22px 24px; margin: 0 0 20px; box-shadow: var(--shadow); }
.lesson h3 { margin: 0 0 6px; font-size: 20px; }
.lesson .lesson-meta { color: var(--muted); font-size: 13.5px; margin-bottom: 12px; }
.lesson h4 { margin: 18px 0 8px; font-size: 16px; color: var(--brand); }
.lesson p, .lesson li { font-size: 14.8px; line-height: 1.75; }
.lesson ol, .lesson ul { margin: 8px 0; padding-left: 22px; }
.lesson .todo-box { background: var(--amber-soft); border-radius: 10px; padding: 12px 16px; margin: 12px 0; font-size: 14px; }
.lesson code { background: #f1f2f8; border-radius: 5px; padding: 1px 6px; font-size: 13px; }
.syllabus table td { font-size: 13.5px; }
.syllabus .wip { color: var(--amber); font-weight: 600; }

/* ---------- Paid unlock ---------- */
.lesson.paid { display: none; }
.paid-gate { max-width: 820px; margin: 0 0 20px; }
.paid-gate .paid-code:focus { outline: 2px solid var(--brand-soft); border-color: var(--brand); }

/* ---------- Quiz ---------- */
.quiz-question { border: 1px solid var(--line); border-radius: 12px; padding: 16px 18px; margin: 14px 0; background: #fbfbff; }
.quiz-q-head { display: flex; align-items: center; margin-bottom: 6px; }
.quiz-q-num { background: var(--brand); color: #fff; font-weight: 700; font-size: 13px; border-radius: 20px; padding: 2px 10px; }
.quiz-q-text { font-size: 15.5px; font-weight: 600; margin: 6px 0 10px; }
.quiz-opts label { display: flex; gap: 10px; align-items: flex-start; border: 1px solid var(--line); background: #fff; border-radius: 10px; padding: 9px 12px; margin: 7px 0; cursor: pointer; font-size: 14.3px; line-height: 1.55; }
.quiz-opts label:hover { border-color: var(--brand); }
.quiz-opts input { margin-top: 4px; accent-color: var(--brand); }
.quiz-opt.right { background: var(--teal-soft); border-color: #2b9a86; }
.quiz-opt.wrong { background: var(--amber-soft); border-color: #e0a03c; }
.quiz-feedback { border-radius: 10px; padding: 10px 14px; margin-top: 8px; font-size: 13.8px; line-height: 1.65; }
.quiz-feedback.note.tip { background: var(--teal-soft); color: #0f4f48; }
.quiz-feedback.note.warn { background: var(--amber-soft); color: #7c4a03; }
.quiz-feedback strong { display: inline; margin-right: 6px; }

/* ---------- Language switcher ---------- */
.lang-switch { margin-left: 10px; }
.lang-select {
  font: inherit; font-size: 13px; padding: 5px 8px; border-radius: 8px;
  border: 1px solid var(--line); background: #fff; color: var(--ink); cursor: pointer;
}
.lang-switch.floating {
  position: fixed; top: 12px; right: 12px; z-index: 999;
  background: #fff; padding: 6px; border-radius: 10px; box-shadow: var(--shadow);
}
@media (max-width: 760px) {
  .lang-switch { width: 100%; margin: 8px 0 0; }
  .lang-switch.floating { width: auto; margin: 0; }
}

/* Hide Google Translate's default banner/UI; we use our own selector */
.goog-te-banner-frame, .goog-te-gadget, #goog-gt-tt, .goog-tooltip, .goog-tooltip:hover { display: none !important; }
body { top: 0 !important; }
.step-done {
  display: inline-flex; align-items: center; gap: 8px; margin-top: 14px;
  font-size: 14px; color: var(--muted); cursor: pointer;
}
.step-done input { accent-color: var(--brand); width: 17px; height: 17px; }

@media (max-width: 560px) {
  .step-card { padding: 18px 16px; }
  .link-box { flex-direction: column; align-items: flex-start; }
  .link-box .url { flex: none; }
  .step-nav { flex-direction: column; }
}