:root {
  color-scheme: light;
  --bg: #f2f1eb;
  --paper: #fbfaf6;
  --paper-strong: #ffffff;
  --ink: #151a16;
  --muted: #626a63;
  --quiet: #858c86;
  --line: #d9ddd8;
  --line-strong: #bec5bf;
  --accent: #166534;
  --accent-soft: #e5f5e9;
  --dark: #0c100d;
  --dark-muted: #9aa49b;
  --radius: 16px;
  --shadow: 0 16px 45px rgba(26, 33, 27, .07);
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body { margin: 0; min-width: 320px; background: var(--bg); color: var(--ink); font-family: Inter, ui-sans-serif, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif; line-height: 1.6; -webkit-font-smoothing: antialiased; }
a { color: inherit; }
button, input { font: inherit; }
.shell { width: min(calc(100% - 48px), 1180px); margin-inline: auto; }
.skip-link { position: fixed; top: 10px; left: 10px; z-index: 30; padding: 10px 14px; background: var(--accent); color: white; transform: translateY(-160%); }
.skip-link:focus { transform: translateY(0); }
.visually-hidden { position: absolute; width: 1px; height: 1px; overflow: hidden; clip: rect(0,0,0,0); white-space: nowrap; }

.course-bar { border-bottom: 1px solid rgba(255,255,255,.1); background: var(--dark); color: white; }
.course-bar-inner { min-height: 66px; display: flex; align-items: center; justify-content: space-between; gap: 28px; }
.wordmark { font-size: .9rem; font-weight: 760; text-decoration: none; letter-spacing: -.03em; }
.course-bar-links { display: flex; align-items: center; gap: 22px; color: var(--dark-muted); font-size: .73rem; }
.course-bar-links a { text-decoration: none; }
.course-bar-links a:hover { color: white; }

.course-hero { padding-block: clamp(62px, 9vw, 112px) 70px; background: var(--dark); color: white; }
.course-hero-grid { display: grid; grid-template-columns: minmax(0, 1.5fr) minmax(270px, .58fr); gap: clamp(46px, 8vw, 110px); align-items: end; }
.course-kicker, .metric-label, .section-kicker, .unit-number, .lesson-number { font-family: "SFMono-Regular", Consolas, monospace; text-transform: uppercase; letter-spacing: .11em; }
.course-kicker { margin: 0; color: var(--course-accent, #63e68c); font-size: .7rem; font-weight: 730; }
.course-hero h1 { max-width: 900px; margin: 18px 0 13px; font-size: clamp(3rem, 7.2vw, 6.4rem); font-weight: 680; line-height: .93; letter-spacing: -.07em; text-wrap: balance; }
.course-title-zh { margin: 0; color: #d9dfda; font-size: clamp(1.02rem, 2vw, 1.34rem); font-weight: 540; }
.course-summary { max-width: 720px; margin: 27px 0 0; color: var(--dark-muted); font-size: 1rem; line-height: 1.78; }
.course-tags { display: flex; flex-wrap: wrap; gap: 8px; margin-top: 25px; }
.course-tag { padding: 5px 9px; border: 1px solid rgba(255,255,255,.13); border-radius: 999px; color: #bdc6be; font-size: .68rem; }
.course-facts { margin: 0; border-top: 3px solid var(--course-accent, #63e68c); }
.course-facts div { padding: 16px 0; border-bottom: 1px solid rgba(255,255,255,.1); }
.course-facts dt { color: var(--dark-muted); font-size: .68rem; }
.course-facts dd { margin: 4px 0 0; font-size: .87rem; font-weight: 620; }

.course-stats { border-bottom: 1px solid var(--line); background: var(--paper); }
.stats-grid { display: grid; grid-template-columns: repeat(4, 1fr); }
.metric { min-height: 126px; padding: 27px 28px; }
.metric + .metric { border-left: 1px solid var(--line); }
.metric-value { display: block; font-size: 1.8rem; font-weight: 740; letter-spacing: -.045em; }
.metric-label { display: block; margin-top: 7px; color: var(--quiet); font-size: .64rem; }
.progress-track { height: 5px; margin-top: 13px; overflow: hidden; border-radius: 99px; background: #e2e5e1; }
.progress-fill { width: 0; height: 100%; background: var(--course-accent, var(--accent)); transition: width .4s ease; }

.dashboard { padding-block: 68px 110px; }
.dashboard-heading { display: flex; align-items: end; justify-content: space-between; gap: 34px; }
.section-kicker { margin: 0; color: var(--accent); font-size: .68rem; font-weight: 730; }
.dashboard-heading h2 { margin: 10px 0 0; font-size: clamp(2.2rem, 4.7vw, 4.2rem); line-height: 1; letter-spacing: -.062em; }
.dashboard-heading > p { max-width: 420px; margin: 0; color: var(--muted); font-size: .86rem; }
.dashboard-tools { display: flex; align-items: center; gap: 16px; margin-top: 34px; padding-block: 18px; border-block: 1px solid var(--line-strong); }
.dashboard-search { flex: 1; }
.dashboard-search input { width: 100%; min-height: 44px; padding: 0 14px; border: 1px solid var(--line); border-radius: 8px; outline: 0; background: var(--paper-strong); color: var(--ink); }
.dashboard-search input:focus { border-color: var(--accent); box-shadow: 0 0 0 3px rgba(22,101,52,.1); }
.view-filters { display: flex; gap: 8px; }
.view-filter { min-height: 36px; padding: 0 12px; border: 1px solid var(--line); border-radius: 999px; background: transparent; color: var(--muted); cursor: pointer; font-size: .72rem; }
.view-filter:hover, .view-filter[aria-pressed="true"] { border-color: var(--accent); color: var(--accent); background: var(--accent-soft); }
.result-status { margin: 16px 0 0; color: var(--quiet); font-family: "SFMono-Regular", Consolas, monospace; font-size: .66rem; text-transform: uppercase; letter-spacing: .09em; }
.path-list { display: grid; gap: 22px; margin-top: 24px; }
.flow-stage { overflow: hidden; border: 1px solid var(--line-strong); border-radius: var(--radius); background: rgba(251, 250, 246, .7); box-shadow: 0 12px 32px rgba(26, 33, 27, .035); }
.stage-heading { display: grid; grid-template-columns: auto 1fr auto; gap: 16px; align-items: baseline; min-height: 60px; padding: 17px 22px; border-bottom: 1px solid var(--line); background: var(--paper); }
.stage-heading p { margin: 0; color: var(--accent); font-family: "SFMono-Regular", Consolas, monospace; font-size: .64rem; font-weight: 760; letter-spacing: .1em; text-transform: uppercase; }
.stage-heading h3 { margin: 0; font-size: 1.02rem; line-height: 1.2; letter-spacing: -.025em; }
.stage-heading > span { color: var(--quiet); font-size: .68rem; }
.flow-grid { display: grid; grid-template-columns: minmax(0, 1.55fr) 42px minmax(210px, .72fr) 42px minmax(210px, .72fr); align-items: stretch; }
.flow-stage.two-lane .flow-grid { grid-template-columns: minmax(0, 1.55fr) 42px minmax(250px, .9fr); }
.flow-lane { min-width: 0; padding: 18px; }
.homework-lane, .exams-lane { border-left: 1px solid rgba(217, 221, 216, .7); }
.homework-lane { background: rgba(22, 101, 52, .025); }
.exams-lane { background: rgba(12, 16, 13, .025); }
.lane-heading { display: flex; align-items: center; justify-content: space-between; gap: 12px; min-height: 28px; margin-bottom: 12px; color: var(--muted); font-family: "SFMono-Regular", Consolas, monospace; font-size: .64rem; letter-spacing: .1em; text-transform: uppercase; }
.lane-heading strong { display: inline-grid; min-width: 25px; height: 25px; place-items: center; border: 1px solid var(--line); border-radius: 999px; background: var(--paper-strong); color: var(--ink); font-size: .62rem; }
.lane-content { display: grid; gap: 10px; align-content: start; }
.work-group { display: grid; gap: 9px; }
.work-group + .work-group { margin-top: 8px; padding-top: 13px; border-top: 1px solid var(--line); }
.work-group-heading { display: flex; align-items: center; justify-content: space-between; gap: 12px; color: var(--muted); font-family: "SFMono-Regular", Consolas, monospace; font-size: .62rem; font-weight: 760; letter-spacing: .07em; text-transform: uppercase; }
.work-group-heading strong { min-width: 24px; padding: 2px 7px; border: 1px solid var(--line); border-radius: 999px; background: var(--paper-strong); color: var(--ink); text-align: center; }
.work-group-items { display: grid; gap: 10px; }
.lectures-lane .lane-content { display: block; }
.flow-arrow { display: grid; min-width: 0; padding-top: 58px; place-items: start center; color: var(--accent); background: linear-gradient(90deg, transparent, rgba(22, 101, 52, .04), transparent); }
.flow-arrow span { display: grid; width: 27px; height: 27px; place-items: center; border: 1px solid rgba(22, 101, 52, .24); border-radius: 999px; background: var(--paper); font-size: .85rem; line-height: 1; }
.lesson-link { display: grid; grid-template-columns: 40px minmax(0, 1fr) minmax(90px, auto) auto; gap: 12px; align-items: center; min-height: 47px; padding: 8px 4px; border-bottom: 1px solid var(--line); color: inherit; text-decoration: none; transition: color .16s ease, background .16s ease; }
.lesson-link:first-child { border-top: 1px solid var(--line); }
.lesson-link:hover { background: rgba(22, 101, 52, .045); color: var(--accent); }
.lesson-number { color: var(--accent); font-family: "SFMono-Regular", Consolas, monospace; font-size: .61rem; font-weight: 760; }
.lesson-title { min-width: 0; font-size: .76rem; font-weight: 650; line-height: 1.35; }
.lesson-detail { overflow: hidden; color: var(--quiet); font-size: .61rem; font-weight: 480; text-align: right; text-overflow: ellipsis; white-space: nowrap; }
.lesson-status { color: var(--quiet); font-size: .6rem; white-space: nowrap; }
.lesson-status.completed { color: var(--accent); }
.flow-card { position: relative; display: flex; min-width: 0; min-height: 148px; flex-direction: column; padding: 17px; border: 1px solid var(--line); border-radius: 12px; background: var(--paper-strong); color: inherit; text-decoration: none; transition: border-color .16s ease, box-shadow .16s ease, transform .16s ease; }
.flow-card[href]:hover { border-color: rgba(22, 101, 52, .38); box-shadow: 0 12px 25px rgba(26, 33, 27, .07); transform: translateY(-2px); }
.exam-card { border-top: 3px solid var(--course-accent, var(--accent)); background: #f7f8f5; }
.card-kicker { margin: 0; color: var(--accent); font-family: "SFMono-Regular", Consolas, monospace; font-size: .61rem; font-weight: 760; letter-spacing: .08em; text-transform: uppercase; }
.flow-card h4 { margin: 13px 0 7px; font-size: .96rem; line-height: 1.28; letter-spacing: -.025em; }
.card-description { margin: 0 0 14px; color: var(--muted); font-size: .7rem; line-height: 1.5; }
.card-meta { display: flex; flex-wrap: wrap; gap: 5px 10px; margin-top: auto; color: var(--quiet); font-size: .61rem; }
.card-action { margin-top: 10px; color: var(--accent); font-size: .68rem; font-weight: 720; }
.lane-empty { display: grid; min-height: 92px; place-items: center; padding: 18px; border: 1px dashed var(--line-strong); border-radius: 10px; color: var(--quiet); font-size: .68rem; text-align: center; }
.flow-stage.is-hidden, [data-card].is-hidden { display: none; }
.flow-lane[hidden], .flow-arrow[hidden] { display: none; }
.empty-state, .load-error { padding: 36px; border: 1px solid var(--line); background: var(--paper); color: var(--muted); }
.course-footer { border-top: 1px solid var(--line); background: var(--paper); }
.course-footer-inner { min-height: 118px; display: flex; align-items: center; justify-content: space-between; gap: 30px; color: var(--quiet); font-size: .72rem; }
.course-footer a { color: var(--accent); }
:focus-visible { outline: 2px solid var(--accent); outline-offset: 4px; }

@media (max-width: 840px) {
  .course-hero-grid { grid-template-columns: 1fr; }
  .course-facts { max-width: 620px; }
  .stats-grid { grid-template-columns: repeat(2, 1fr); }
  .metric:nth-child(3) { border-left: 0; border-top: 1px solid var(--line); }
  .metric:nth-child(4) { border-top: 1px solid var(--line); }
  .dashboard-heading { align-items: start; flex-direction: column; }
  .flow-grid, .flow-stage.two-lane .flow-grid { grid-template-columns: 1fr; }
  .flow-arrow { min-height: 38px; padding-top: 0; place-items: center; background: linear-gradient(180deg, transparent, rgba(22, 101, 52, .04), transparent); }
  .flow-arrow span { transform: rotate(90deg); }
  .homework-lane, .exams-lane { border-top: 1px solid var(--line); border-left: 0; }
}
@media (max-width: 640px) {
  .shell { width: min(calc(100% - 32px), 1180px); }
  .course-bar-links a:not(:first-child) { display: none; }
  .course-hero { padding-block: 54px 58px; }
  .course-hero h1 { font-size: clamp(2.8rem, 15vw, 4.9rem); }
  .metric { min-height: 108px; padding: 22px 18px; }
  .dashboard { padding-block: 54px 76px; }
  .dashboard-tools { align-items: stretch; flex-direction: column; }
  .view-filters { flex-wrap: wrap; }
  .stage-heading { grid-template-columns: 1fr auto; gap: 4px 12px; padding-inline: 16px; }
  .stage-heading p { grid-column: 1 / -1; }
  .flow-lane { padding: 14px; }
  .lesson-link { grid-template-columns: 34px minmax(0, 1fr) auto; min-height: 45px; padding: 8px 2px; }
  .lesson-title { font-size: .72rem; }
  .lesson-detail { display: none; }
  .course-footer-inner { align-items: flex-start; flex-direction: column; justify-content: center; }
}
@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  *, *::before, *::after { transition-duration: .01ms !important; }
}