:root {
  --bg: #fbfaf7;
  --paper: #ffffff;
  --surface: #f5f6f8;
  --surface-blue: #f3f7ff;
  --ink: #111827;
  --muted: #5f6673;
  --faint: #8a909c;
  --line: #dfe1e5;
  --line-strong: #c9cdd4;
  --blue: #1557e8;
  --blue-strong: #0d46c8;
  --blue-soft: #eaf1ff;
  --coral: #ef5a52;
  --coral-soft: #fff2ef;
  --green: #19704c;
  --green-soft: #eaf7f0;
  --radius: 10px;
  --header-h: 64px;
  --sidebar-w: 248px;
  --notes-w: 344px;
  --font: "Inter", "Noto Sans SC", "PingFang SC", "Microsoft YaHei", system-ui, sans-serif;
  --display: "Aptos Display", "Noto Sans SC", "PingFang SC", var(--font);
}

* { box-sizing: border-box; }

html {
  scroll-behavior: smooth;
  background: var(--bg);
}

body {
  margin: 0;
  min-width: 320px;
  color: var(--ink);
  background:
    linear-gradient(rgba(255,255,255,.48), rgba(255,255,255,.48)),
    var(--bg);
  font-family: var(--font);
  font-size: 16px;
  line-height: 1.72;
  -webkit-font-smoothing: antialiased;
}

button, textarea, input { font: inherit; }
button, a { -webkit-tap-highlight-color: transparent; }
a { color: var(--blue); }

.topbar {
  position: sticky;
  z-index: 30;
  top: 0;
  height: var(--header-h);
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 24px;
  padding: 0 28px;
  background: rgba(251, 250, 247, .95);
  border-bottom: 1px solid var(--line);
  backdrop-filter: blur(12px);
}

.brand {
  color: var(--ink);
  text-decoration: none;
  font-family: var(--display);
  font-size: 24px;
  font-weight: 850;
  letter-spacing: -.03em;
}

.top-meta {
  display: flex;
  align-items: center;
  gap: 9px;
  color: var(--muted);
  font-size: 14px;
}

.top-meta svg { width: 18px; height: 18px; }

.course-shell {
  display: grid;
  grid-template-columns: var(--sidebar-w) minmax(0, 1fr) var(--notes-w);
  min-height: calc(100vh - var(--header-h));
}

.course-sidebar {
  position: sticky;
  top: var(--header-h);
  height: calc(100vh - var(--header-h));
  overflow-y: auto;
  border-right: 1px solid var(--line);
  background: rgba(251, 250, 247, .9);
  padding: 32px 0 24px;
}

.progress-block { padding: 0 28px 23px; }

.progress-label {
  display: flex;
  justify-content: space-between;
  color: var(--ink);
  font-size: 15px;
  font-weight: 720;
}

.progress-label span:last-child {
  color: var(--muted);
  font-variant-numeric: tabular-nums;
}

.progress-track {
  height: 7px;
  margin-top: 13px;
  overflow: hidden;
  border-radius: 99px;
  background: #dedede;
}

.progress-fill {
  width: var(--course-progress, 16.66%);
  height: 100%;
  border-radius: inherit;
  background: var(--blue);
  transition: width .35s ease;
}

.lesson-list {
  display: flex;
  flex-direction: column;
}

.lesson-link {
  position: relative;
  display: grid;
  grid-template-columns: 24px 30px 1fr;
  align-items: center;
  gap: 9px;
  min-height: 68px;
  padding: 11px 22px 11px 28px;
  color: #4b4f57;
  text-decoration: none;
  font-size: 15px;
  line-height: 1.35;
}

.lesson-link:hover { background: rgba(21, 87, 232, .04); }

.lesson-link.active {
  color: var(--blue);
  background: var(--blue-soft);
  font-weight: 760;
}

.lesson-link.active::before {
  content: "";
  position: absolute;
  inset: 0 auto 0 0;
  width: 4px;
  background: var(--blue);
}

.lesson-dot {
  width: 20px;
  height: 20px;
  display: grid;
  place-items: center;
  border: 1.5px solid #6f747c;
  border-radius: 50%;
}

.lesson-link.active .lesson-dot { border-color: var(--blue); }
.lesson-link.active .lesson-dot::after,
.lesson-link.completed .lesson-dot::after {
  content: "";
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background: currentColor;
}

.lesson-link.completed .lesson-dot { color: var(--green); border-color: var(--green); }

.lesson-number {
  font-size: 15px;
  font-weight: 700;
  font-variant-numeric: tabular-nums;
}

.sidebar-map {
  display: flex;
  align-items: center;
  gap: 12px;
  margin: 16px 28px 0;
  padding: 22px 0;
  border-top: 1px solid var(--line);
  color: var(--blue);
  text-decoration: none;
  font-size: 14px;
  font-weight: 700;
}

.sidebar-map svg { width: 22px; height: 22px; }

.lesson-main {
  min-width: 0;
  padding: 0 30px 72px;
}

.lesson-content {
  width: min(100%, 850px);
  margin: 0 auto;
}

.lesson-hero {
  padding: 40px 0 27px;
  border-bottom: 1px solid var(--line);
}

.lesson-hero h1 {
  position: relative;
  width: fit-content;
  max-width: 100%;
  margin: 0;
  font-family: var(--display);
  font-size: clamp(32px, 3.15vw, 48px);
  line-height: 1.2;
  letter-spacing: -.045em;
  font-weight: 850;
}

.lesson-hero h1::after {
  content: "";
  position: absolute;
  right: 0;
  bottom: -9px;
  width: 47%;
  height: 8px;
  border-top: 2px solid var(--blue);
  border-radius: 50%;
  transform: rotate(2deg);
}

.lesson-hero p {
  max-width: 720px;
  margin: 19px 0 0;
  color: var(--muted);
  font-size: 18px;
}

.hero-actions {
  display: flex;
  align-items: center;
  gap: 24px;
  margin-top: 25px;
}

.btn {
  min-height: 48px;
  padding: 0 22px;
  border: 1px solid transparent;
  border-radius: 7px;
  cursor: pointer;
  font-size: 15px;
  font-weight: 740;
  transition: transform .16s ease, background .16s ease, border-color .16s ease;
}

.btn:hover { transform: translateY(-1px); }
.btn:focus-visible, .option:focus-visible, .quiz-option:focus-visible,
.hint-toggle:focus-visible, textarea:focus-visible, a:focus-visible {
  outline: 3px solid rgba(21, 87, 232, .25);
  outline-offset: 3px;
}

.btn-primary { color: #fff; background: var(--blue); }
.btn-primary:hover { background: var(--blue-strong); }
.btn-secondary { color: var(--ink); background: var(--paper); border-color: var(--line-strong); }
.btn-quiet { padding: 0; color: var(--blue); background: transparent; }

.learning-section {
  position: relative;
  padding: 34px 0 4px 68px;
}

.section-number {
  position: absolute;
  top: 33px;
  left: 0;
  width: 43px;
  height: 43px;
  display: grid;
  place-items: center;
  color: var(--blue);
  border: 1.7px solid var(--blue);
  border-radius: 50%;
  font-family: Georgia, serif;
  font-size: 26px;
  font-style: italic;
  line-height: 1;
  transform: rotate(-6deg);
}

.learning-section:not(:last-child)::before {
  content: "";
  position: absolute;
  top: 79px;
  bottom: -26px;
  left: 21px;
  border-left: 1px dashed var(--line-strong);
}

.learning-section h2 {
  margin: 0;
  font-family: var(--display);
  font-size: 24px;
  line-height: 1.35;
  letter-spacing: -.025em;
}

.learning-section h3 {
  margin: 24px 0 8px;
  font-size: 18px;
  line-height: 1.45;
}

.learning-section > p,
.body-copy p { color: #444a55; }

.lede { margin: 5px 0 18px; color: var(--muted) !important; }

.story-card,
.insight-box,
.scenario,
.practice-card,
.reading-item {
  border: 1px solid var(--line);
  background: var(--paper);
  border-radius: var(--radius);
}

.story-card {
  padding: 20px 22px;
  border-left: 3px solid var(--blue);
}

.story-card strong,
.scenario-label {
  color: var(--blue);
  font-size: 13px;
  letter-spacing: .01em;
}

.insight-box {
  margin: 18px 0;
  padding: 18px 20px;
  background: var(--surface-blue);
}

.insight-box strong { color: var(--blue-strong); }

.scenario {
  margin: 18px 0 14px;
  padding: 16px 18px;
  background: var(--surface-blue);
  border-color: #bcd0ff;
}

.scenario p { margin: 4px 0 0; color: var(--ink); line-height: 1.65; }

.option-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 13px;
  margin-top: 12px;
}

.option {
  min-height: 134px;
  padding: 16px;
  color: var(--ink);
  text-align: left;
  background: var(--paper);
  border: 1px solid var(--line-strong);
  border-radius: 8px;
  cursor: pointer;
  transition: border-color .16s ease, box-shadow .16s ease, transform .16s ease;
}

.option:hover { transform: translateY(-2px); border-color: #94afea; }
.option.selected { border: 2px solid var(--blue); background: #fbfdff; box-shadow: 0 0 0 3px rgba(21,87,232,.08); }
.option.correct { border: 2px solid var(--green); background: var(--green-soft); }
.option.wrong { border: 2px solid var(--coral); background: var(--coral-soft); }

.option-title {
  display: flex;
  gap: 9px;
  align-items: flex-start;
  font-size: 14px;
  font-weight: 760;
  line-height: 1.45;
}

.option-radio {
  width: 18px;
  height: 18px;
  flex: 0 0 auto;
  margin-top: 1px;
  border: 1.5px solid #757b85;
  border-radius: 50%;
}

.option.selected .option-radio,
.option.correct .option-radio {
  border: 5px solid var(--blue);
}

.option.correct .option-radio { border-color: var(--green); }

.option-desc {
  display: block;
  margin: 8px 0 0 27px;
  color: var(--muted);
  font-size: 13px;
  line-height: 1.6;
}

.feedback {
  display: none;
  gap: 14px;
  align-items: flex-start;
  margin-top: 14px;
  padding: 14px 16px;
  border: 1px solid #f2a49f;
  border-radius: 8px;
  color: #a93630;
  background: var(--coral-soft);
  font-size: 14px;
}

.feedback.show { display: flex; animation: rise .25s ease both; }
.feedback.success { color: var(--green); border-color: #9ccdb4; background: var(--green-soft); }
.feedback-icon { font-size: 19px; line-height: 1.4; }
.feedback strong { display: block; margin-bottom: 2px; }

.pipeline {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  margin: 18px 0;
  border: 1px solid var(--line-strong);
  border-radius: var(--radius);
  overflow: hidden;
}

.pipeline-step {
  position: relative;
  padding: 18px 16px;
  background: var(--paper);
}

.pipeline-step:not(:last-child) { border-right: 1px solid var(--line); }
.pipeline-step b { display: block; margin-bottom: 5px; color: var(--blue); font-size: 14px; }
.pipeline-step span { color: var(--muted); font-size: 13px; line-height: 1.5; }

.compare-table {
  width: 100%;
  margin: 18px 0;
  border-collapse: separate;
  border-spacing: 0;
  overflow: hidden;
  border: 1px solid var(--line-strong);
  border-radius: var(--radius);
  font-size: 13px;
}

.compare-table th,
.compare-table td {
  padding: 10px 12px;
  border-right: 1px solid var(--line);
  border-bottom: 1px solid var(--line);
  text-align: left;
  vertical-align: top;
}

.compare-table th { background: var(--surface); font-weight: 750; }
.compare-table th:last-child, .compare-table td:last-child { border-right: 0; }
.compare-table tr:last-child td { border-bottom: 0; }

.sortable {
  display: flex;
  flex-direction: column;
  gap: 9px;
  margin: 14px 0;
}

.sort-item {
  display: grid;
  grid-template-columns: 30px 1fr auto;
  align-items: center;
  gap: 12px;
  padding: 12px 14px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--paper);
}

.sort-index {
  width: 27px;
  height: 27px;
  display: grid;
  place-items: center;
  border-radius: 50%;
  color: var(--blue);
  background: var(--blue-soft);
  font-size: 13px;
  font-weight: 800;
}

.sort-controls { display: flex; gap: 6px; }
.sort-controls button {
  width: 31px;
  height: 31px;
  color: var(--muted);
  border: 1px solid var(--line);
  border-radius: 6px;
  background: var(--paper);
  cursor: pointer;
}

.sort-controls button:hover { color: var(--blue); border-color: #9bb5ee; }

.meter-row {
  display: grid;
  grid-template-columns: 120px 1fr 48px;
  align-items: center;
  gap: 12px;
  margin: 13px 0;
  font-size: 14px;
}

.meter {
  height: 10px;
  overflow: hidden;
  border-radius: 99px;
  background: #e6e7e9;
}

.meter > span {
  display: block;
  width: var(--value);
  height: 100%;
  border-radius: inherit;
  background: var(--blue);
  transition: width .4s ease;
}

.quiz {
  margin: 18px 0;
  padding: 20px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--paper);
}

.quiz-question { margin: 0 0 14px; font-weight: 740; }

.quiz-options {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 9px;
}

.quiz-option {
  min-height: 44px;
  padding: 10px 12px;
  text-align: left;
  color: #383e48;
  border: 1px solid var(--line);
  border-radius: 7px;
  background: var(--paper);
  cursor: pointer;
  font-size: 14px;
}

.quiz-option:hover { border-color: #9bb5ee; }
.quiz-option.correct { color: var(--green); border-color: #88bca2; background: var(--green-soft); }
.quiz-option.wrong { color: #a93630; border-color: #e6a19c; background: var(--coral-soft); }
.quiz-result { display: none; margin-top: 11px; color: var(--muted); font-size: 13px; }
.quiz-result.show { display: block; }

.practice-card { margin: 18px 0; padding: 20px; }
.practice-card h3 { margin-top: 0; }

.hint-toggle {
  min-height: 40px;
  padding: 0 14px;
  color: var(--blue);
  border: 1px solid #a9bff0;
  border-radius: 7px;
  background: var(--surface-blue);
  cursor: pointer;
  font-size: 14px;
  font-weight: 700;
}

.hint-content {
  display: none;
  margin-top: 12px;
  padding: 14px 16px;
  color: var(--muted);
  border-left: 2px solid var(--blue);
  background: var(--surface-blue);
  font-size: 14px;
}

.hint-content.show { display: block; }
.exercise-hidden { display: none; }

.reading-list {
  display: flex;
  flex-direction: column;
  gap: 10px;
  margin-top: 15px;
}

.reading-item { padding: 15px 18px; }
.reading-item a { font-size: 14px; font-weight: 750; text-decoration: none; }
.reading-item a:hover { text-decoration: underline; }
.reading-meta { margin-top: 3px; color: var(--faint); font-size: 12px; }
.reading-desc { margin-top: 4px; color: var(--muted); font-size: 13px; }

.lesson-nav {
  display: flex;
  justify-content: space-between;
  gap: 16px;
  margin: 46px 0 0 68px;
  padding-top: 24px;
  border-top: 1px solid var(--line);
}

.lesson-nav a, .lesson-nav span {
  max-width: 48%;
  color: var(--muted);
  text-decoration: none;
  font-size: 14px;
}

.lesson-nav a:hover { color: var(--blue); }

.task-panel {
  position: sticky;
  top: var(--header-h);
  height: calc(100vh - var(--header-h));
  overflow-y: auto;
  padding: 20px 18px;
  border-left: 1px solid var(--line);
  background: rgba(255, 255, 255, .55);
}

.task-card {
  display: flex;
  flex-direction: column;
  min-height: calc(100vh - var(--header-h) - 40px);
  padding: 18px;
  border: 1px solid var(--line-strong);
  border-radius: var(--radius);
  background: rgba(255,255,255,.68);
}

.task-head {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
}

.task-head h2 { margin: 0; font-size: 18px; }
.task-head svg { width: 20px; color: var(--muted); }
.task-card > p { margin: 14px 0 4px; color: #343a44; font-size: 14px; }
.task-tip { color: var(--muted) !important; }

.note-area {
  width: 100%;
  min-height: 258px;
  flex: 1 1 260px;
  margin-top: 12px;
  padding: 15px;
  resize: vertical;
  color: var(--ink);
  border: 1px solid var(--line);
  border-radius: 8px;
  background: rgba(255,255,255,.84);
  font-size: 14px;
  line-height: 1.65;
}

.note-editor {
  display: flex;
  flex: 1 1 300px;
  flex-direction: column;
  min-height: 300px;
  margin-top: 12px;
  overflow: hidden;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: rgba(255,255,255,.84);
}

.note-editor .note-area {
  min-height: 220px;
  flex: 1 1 auto;
  margin: 0;
  border: 0;
  border-radius: 0;
  background: transparent;
}

.note-editor .note-area:focus-visible {
  outline: 0;
  box-shadow: inset 0 0 0 2px rgba(21,87,232,.2);
}

.note-toolbar {
  display: flex;
  gap: 2px;
  align-items: center;
  min-height: 43px;
  padding: 0 10px;
  border-bottom: 1px solid var(--line);
  background: #fcfcfc;
}

.note-toolbar button {
  width: 32px;
  height: 32px;
  color: #3e4652;
  border: 0;
  border-radius: 5px;
  background: transparent;
  cursor: pointer;
  font-size: 14px;
}

.note-toolbar button:hover { color: var(--blue); background: var(--blue-soft); }
.note-toolbar .toolbar-divider { width: 1px; height: 20px; margin: 0 5px; background: var(--line); }

.note-count {
  margin-top: -30px;
  padding-right: 12px;
  position: relative;
  align-self: flex-end;
  color: var(--faint);
  font-size: 12px;
  pointer-events: none;
}

.writing-guide {
  margin-top: 22px;
  padding: 14px 14px 9px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: #fafafa;
}

.writing-guide strong { font-size: 13px; }
.writing-guide ul { margin: 8px 0; padding-left: 19px; color: var(--muted); font-size: 12px; }

.save-note { width: 100%; margin-top: 18px; }
.autosave { margin: 9px 0 0 !important; text-align: center; color: var(--faint) !important; font-size: 12px !important; }

.mobile-progress {
  display: none;
  padding: 10px 18px;
  border-bottom: 1px solid var(--line);
  background: var(--paper);
}

.map-dialog {
  width: min(760px, calc(100vw - 32px));
  padding: 0;
  border: 1px solid var(--line-strong);
  border-radius: 14px;
  background: var(--bg);
  box-shadow: 0 24px 80px rgba(17,24,39,.18);
}

.map-dialog::backdrop { background: rgba(17,24,39,.42); backdrop-filter: blur(3px); }
.map-dialog header { display: flex; justify-content: space-between; align-items: center; padding: 22px 24px; border-bottom: 1px solid var(--line); }
.map-dialog h2 { margin: 0; font-size: 22px; }
.map-dialog .dialog-close { width: 38px; height: 38px; border: 1px solid var(--line); border-radius: 50%; background: var(--paper); cursor: pointer; }
.map-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 0; padding: 10px 24px 24px; }
.map-node { position: relative; padding: 22px 24px 18px 52px; border-bottom: 1px solid var(--line); }
.map-node::before { content: attr(data-number); position: absolute; left: 5px; top: 21px; width: 34px; height: 34px; display: grid; place-items: center; color: var(--blue); border: 1px solid var(--blue); border-radius: 50%; font-size: 12px; font-weight: 800; }
.map-node a { color: var(--ink); font-weight: 760; text-decoration: none; }
.map-node p { margin: 4px 0 0; color: var(--muted); font-size: 12px; line-height: 1.55; }

.course-home {
  min-height: 100vh;
  padding: 40px;
  display: grid;
  place-items: center;
}

.home-sheet { width: min(1060px, 100%); }
.home-sheet h1 { max-width: 760px; margin: 0; font-size: clamp(44px, 7vw, 82px); line-height: 1.06; letter-spacing: -.055em; }
.home-sheet > p { max-width: 660px; margin: 22px 0 0; color: var(--muted); font-size: 20px; }
.home-actions { display: flex; gap: 18px; align-items: center; margin: 30px 0 48px; }
.home-map { display: grid; grid-template-columns: repeat(3, 1fr); border-top: 1px solid var(--line-strong); border-left: 1px solid var(--line-strong); }
.home-lesson { min-height: 190px; padding: 22px; color: var(--ink); text-decoration: none; border-right: 1px solid var(--line-strong); border-bottom: 1px solid var(--line-strong); background: rgba(255,255,255,.52); }
.home-lesson:hover { background: var(--surface-blue); }
.home-lesson span { color: var(--blue); font-size: 13px; font-weight: 800; }
.home-lesson h2 { margin: 25px 0 8px; font-size: 20px; line-height: 1.35; }
.home-lesson p { margin: 0; color: var(--muted); font-size: 13px; }

@keyframes rise {
  from { opacity: 0; transform: translateY(5px); }
  to { opacity: 1; transform: translateY(0); }
}

@media (max-width: 1180px) {
  :root { --sidebar-w: 220px; --notes-w: 300px; }
  .lesson-main { padding-inline: 22px; }
  .task-panel { padding-inline: 12px; }
  .task-card { padding: 15px; }
  .learning-section { padding-left: 58px; }
  .option-grid { grid-template-columns: 1fr; }
  .option { min-height: 0; }
}

@media (max-width: 920px) {
  .course-shell { grid-template-columns: 190px minmax(0, 1fr); }
  .task-panel { position: static; height: auto; grid-column: 2; padding: 0 22px 44px; border-left: 0; }
  .task-card { min-height: auto; max-width: 850px; margin: 0 auto; }
  .note-area { min-height: 220px; }
  .note-editor { min-height: 260px; }
  .lesson-link { grid-template-columns: 20px 1fr; padding-inline: 20px 12px; }
  .lesson-link .lesson-number { display: none; }
  .home-map { grid-template-columns: 1fr 1fr; }
}

@media (max-width: 700px) {
  .topbar { height: 56px; padding: 0 16px; }
  .brand { font-size: 20px; }
  .top-meta { font-size: 12px; }
  .course-shell { display: block; }
  .course-sidebar { display: none; }
  .mobile-progress { display: block; position: sticky; top: 56px; z-index: 25; }
  .lesson-main { padding: 0 18px 46px; }
  .lesson-hero { padding-top: 30px; }
  .lesson-hero h1 { font-size: 34px; }
  .lesson-hero p { font-size: 16px; }
  .hero-actions { align-items: stretch; flex-direction: column; gap: 8px; }
  .btn-quiet { text-align: left; }
  .learning-section { padding: 28px 0 0 48px; }
  .section-number { top: 27px; width: 35px; height: 35px; font-size: 21px; }
  .learning-section:not(:last-child)::before { left: 17px; top: 68px; }
  .learning-section h2 { font-size: 21px; }
  .pipeline { grid-template-columns: 1fr; }
  .pipeline-step:not(:last-child) { border-right: 0; border-bottom: 1px solid var(--line); }
  .quiz-options { grid-template-columns: 1fr; }
  .compare-table { display: block; overflow-x: auto; white-space: nowrap; }
  .meter-row { grid-template-columns: 90px 1fr 38px; }
  .lesson-nav { margin-left: 0; }
  .task-panel { padding: 0 18px 40px; }
  .map-grid { grid-template-columns: 1fr; }
  .home-map { grid-template-columns: 1fr; }
  .course-home { padding: 24px 18px; }
  .home-sheet h1 { font-size: 48px; }
  .home-sheet > p { font-size: 17px; }
  .home-actions { align-items: stretch; flex-direction: column; }
}

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