:root {
  --bg: #f3f6fb;
  --ink: #182033;
  --muted: #667085;
  --panel: #ffffff;
  --line: #d7dfec;
  --accent: #178b8f;
  --accent-dark: #0b686f;
  --soft: #e8f6f5;
  --warn: #c15f18;
  --danger: #bf3434;
  --success: #227447;
  --gold: #f0b84f;
  --violet: #6b5bd2;
  --shadow: 0 18px 42px rgba(24, 32, 51, 0.08);
  font-family: "Segoe UI", "Microsoft YaHei", Arial, sans-serif;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-height: 100vh;
  background:
    linear-gradient(180deg, rgba(232, 246, 245, 0.78) 0%, rgba(243, 246, 251, 0.8) 260px),
    var(--bg);
  color: var(--ink);
}

a {
  color: inherit;
}

.layout {
  display: grid;
  grid-template-columns: 260px minmax(0, 1fr);
  min-height: 100vh;
}

.side {
  position: sticky;
  top: 0;
  height: 100vh;
  background:
    linear-gradient(180deg, #1f2a44 0%, #172033 100%);
  color: #fff;
  padding: 24px 18px;
  box-shadow: 12px 0 30px rgba(24, 32, 51, 0.16);
}

.brand {
  display: flex;
  align-items: center;
  gap: 12px;
  margin-bottom: 26px;
}

.brand-mark {
  display: grid;
  width: 46px;
  height: 46px;
  place-items: center;
  border-radius: 12px;
  background: linear-gradient(135deg, #ffd166 0%, #f0b84f 100%);
  color: #20283a;
  font-weight: 800;
  box-shadow: 0 10px 22px rgba(240, 184, 79, 0.25);
}

.brand strong,
.brand span {
  display: block;
}

.brand span:last-child {
  color: #b8c3d9;
  font-size: 13px;
  margin-top: 3px;
}

.nav {
  display: grid;
  gap: 7px;
}

.nav a {
  display: block;
  min-height: 42px;
  padding: 11px 12px;
  border-radius: 10px;
  color: #eef4ff;
  text-decoration: none;
  font-weight: 700;
  border: 1px solid transparent;
  transition: background 0.18s ease, border-color 0.18s ease, transform 0.18s ease;
}

.nav a:hover,
.nav a.active {
  background: rgba(23, 139, 143, 0.38);
  border-color: rgba(255, 255, 255, 0.12);
  transform: translateX(2px);
}

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

.topbar {
  display: flex;
  justify-content: space-between;
  gap: 18px;
  align-items: flex-start;
  margin-bottom: 22px;
  padding: 4px 0;
}

.eyebrow {
  margin: 0 0 6px;
  color: var(--accent-dark);
  font-weight: 800;
}

h1 {
  margin: 0;
  font-size: 36px;
  line-height: 1.18;
  letter-spacing: 0;
}

.lead {
  max-width: 820px;
  margin: 10px 0 0;
  color: var(--muted);
  line-height: 1.7;
}

.primary-link,
.ghost-link {
  display: inline-flex;
  min-height: 42px;
  align-items: center;
  justify-content: center;
  padding: 0 15px;
  border-radius: 10px;
  text-decoration: none;
  font-weight: 800;
  border: 1px solid transparent;
  transition: transform 0.18s ease, filter 0.18s ease, box-shadow 0.18s ease;
}

.primary-link {
  background: linear-gradient(135deg, var(--accent) 0%, var(--accent-dark) 100%);
  color: #fff;
  box-shadow: 0 12px 24px rgba(23, 139, 143, 0.18);
}

.ghost-link {
  background: #e8edf6;
  color: var(--ink);
  border-color: #dbe3f0;
}

.primary-link:hover,
.ghost-link:hover {
  transform: translateY(-1px);
  filter: brightness(0.98);
}

.actions {
  display: flex;
  gap: 10px;
  flex-wrap: wrap;
}

.grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 14px;
}

.grid.two {
  grid-template-columns: repeat(2, minmax(0, 1fr));
}

.card {
  min-width: 0;
  border: 1px solid var(--line);
  border-radius: 12px;
  background: var(--panel);
  padding: 18px;
  box-shadow: 0 10px 26px rgba(24, 32, 51, 0.05);
}

.card h2,
.card h3 {
  margin: 0 0 10px;
}

.card p {
  margin: 0;
  color: var(--muted);
  line-height: 1.65;
}

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

.metric strong {
  font-size: 28px;
}

.tag-row {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
  margin-top: 12px;
}

.tag {
  display: inline-flex;
  min-height: 28px;
  align-items: center;
  padding: 0 9px;
  border-radius: 999px;
  background: var(--soft);
  color: var(--accent-dark);
  font-size: 13px;
  font-weight: 700;
  border: 1px solid rgba(23, 139, 143, 0.1);
}

.progress {
  height: 10px;
  border-radius: 999px;
  background: #e8edf6;
  overflow: hidden;
  margin-top: 12px;
}

.progress span {
  display: block;
  height: 100%;
  border-radius: inherit;
  background: var(--accent);
}

.list {
  display: grid;
  gap: 10px;
  margin: 0;
  padding: 0;
  list-style: none;
}

.list li {
  display: flex;
  justify-content: space-between;
  gap: 12px;
  align-items: center;
  min-height: 46px;
  padding: 10px 12px;
  border-radius: 10px;
  background: #f8fafc;
}

.status {
  color: var(--accent-dark);
  font-size: 13px;
  font-weight: 800;
  white-space: nowrap;
}

.danger {
  color: var(--danger);
}

.warn {
  color: var(--warn);
}

.success {
  color: var(--success);
}

.section-title {
  margin: 24px 0 12px;
  font-size: 22px;
}

.course-list,
.exercise-list,
.lesson-timeline {
  display: grid;
  gap: 14px;
}

.course-card,
.exercise-card,
.timeline-item {
  border: 1px solid var(--line);
  border-radius: 12px;
  background: var(--panel);
  padding: 18px;
  box-shadow: 0 12px 26px rgba(24, 32, 51, 0.05);
}

.course-card {
  display: grid;
  grid-template-columns: minmax(0, 1fr) auto;
  gap: 14px;
  align-items: center;
}

.course-card-header {
  display: flex;
  gap: 14px;
  align-items: flex-start;
}

.course-number,
.timeline-item > span {
  display: grid;
  width: 42px;
  height: 42px;
  place-items: center;
  border-radius: 10px;
  background: var(--soft);
  color: var(--accent-dark);
  font-weight: 800;
  flex: 0 0 auto;
}

.course-card h2,
.exercise-card h3,
.timeline-item h3 {
  margin: 0 0 6px;
}

.course-card p,
.exercise-card p,
.timeline-item p {
  margin: 0;
  color: var(--muted);
  line-height: 1.6;
}

.course-actions {
  display: flex;
  gap: 10px;
  flex-wrap: wrap;
  justify-content: flex-end;
}

.compact-list {
  margin: 0;
  padding-left: 18px;
  color: var(--muted);
  line-height: 1.7;
}

.timeline-item {
  display: flex;
  gap: 14px;
  align-items: flex-start;
}

.slide-deck {
  display: grid;
  gap: 12px;
}

.slide-stage {
  min-height: 430px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: linear-gradient(135deg, #ffffff 0%, #f8fbff 100%);
  padding: 18px;
  display: grid;
  grid-template-rows: auto auto minmax(240px, 1fr) auto;
  gap: 14px;
}

.slide-topline,
.slide-footer,
.slide-controls {
  display: flex;
  gap: 10px;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
}

.slide-controls {
  justify-content: flex-start;
}

.slide-progress {
  height: 8px;
  border-radius: 999px;
  background: #e8edf6;
  overflow: hidden;
}

.slide-progress span {
  display: block;
  height: 100%;
  width: 0;
  border-radius: inherit;
  background: var(--accent);
  transition: width 0.2s ease;
}

.slide-body {
  display: grid;
  align-content: center;
  gap: 14px;
  padding: 28px;
  border-radius: 8px;
  background: #ffffff;
  border: 1px solid var(--line);
}

.slide-kicker {
  color: var(--accent-dark);
  font-weight: 900;
}

.slide-body h3 {
  margin: 0;
  font-size: 30px;
  line-height: 1.25;
}

.slide-body p {
  margin: 0;
  color: var(--muted);
  line-height: 1.75;
  font-size: 17px;
}

.slide-body ul {
  display: grid;
  gap: 8px;
  margin: 0;
  padding-left: 22px;
  color: var(--ink);
  line-height: 1.65;
}

.slide-footer span {
  color: var(--muted);
  font-size: 13px;
  font-weight: 700;
}

.slide-dots {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
}

.slide-dot {
  width: 28px;
  height: 8px;
  border: 0;
  border-radius: 999px;
  background: #cfd8e8;
  cursor: pointer;
}

.slide-dot.active {
  background: var(--accent);
}

.video-course {
  display: grid;
  grid-template-columns: minmax(0, 1.5fr) minmax(280px, 0.75fr);
  gap: 16px;
  align-items: start;
}

.video-player {
  border: 1px solid var(--line);
  border-radius: 14px;
  background: var(--panel);
  overflow: hidden;
  box-shadow: var(--shadow);
}

.video-screen {
  min-height: 480px;
  display: grid;
  grid-template-rows: auto minmax(260px, 1fr) auto;
  gap: 16px;
  padding: 20px;
  background:
    radial-gradient(circle at 20% 20%, rgba(23, 139, 143, 0.22), transparent 32%),
    linear-gradient(145deg, #101827 0%, #1b2440 58%, #102f35 100%);
  color: #f8fafc;
}

.video-topbar,
.video-controls {
  display: flex;
  gap: 10px;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
}

.video-visual {
  display: grid;
  grid-template-columns: 120px minmax(0, 1fr);
  gap: 24px;
  align-items: center;
  padding: 30px;
  border: 1px solid rgba(255, 255, 255, 0.14);
  border-radius: 14px;
  background: rgba(255, 255, 255, 0.07);
  backdrop-filter: blur(8px);
}

.video-visual span {
  display: grid;
  width: 108px;
  height: 108px;
  place-items: center;
  border-radius: 16px;
  background: linear-gradient(135deg, #ffd166 0%, #f0b84f 100%);
  color: #20283a;
  font-size: 42px;
  font-weight: 900;
  box-shadow: 0 18px 34px rgba(240, 184, 79, 0.24);
}

.video-visual h3 {
  margin: 0 0 10px;
  font-size: 32px;
  line-height: 1.24;
}

.video-visual p,
.video-caption {
  margin: 0;
  color: #dbeafe;
  line-height: 1.75;
}

.video-caption {
  min-height: 92px;
  padding: 14px;
  border-radius: 12px;
  background: rgba(255, 255, 255, 0.08);
  border: 1px solid rgba(255, 255, 255, 0.1);
}

.video-progress {
  height: 8px;
  background: #e8edf6;
  overflow: hidden;
}

.video-progress span {
  display: block;
  width: 0;
  height: 100%;
  background: var(--accent);
  transition: width 0.25s ease;
}

.video-controls {
  padding: 12px;
  background: #ffffff;
}

.video-controls span {
  color: var(--muted);
  font-size: 13px;
  font-weight: 700;
}

.video-sidebar {
  display: grid;
  gap: 14px;
}

.chapter-list {
  display: grid;
  gap: 8px;
}

.chapter-item {
  display: grid;
  grid-template-columns: 32px minmax(0, 1fr);
  gap: 10px;
  align-items: start;
  width: 100%;
  border: 1px solid var(--line);
  border-radius: 10px;
  background: #f8fafc;
  color: var(--ink);
  cursor: pointer;
  padding: 10px;
  text-align: left;
}

.chapter-item span {
  display: grid;
  width: 32px;
  height: 32px;
  place-items: center;
  border-radius: 10px;
  background: #e8edf6;
  color: var(--accent-dark);
  font-weight: 900;
}

.chapter-item strong,
.chapter-item small {
  display: block;
}

.chapter-item small {
  margin-top: 3px;
  color: var(--muted);
  line-height: 1.45;
}

.chapter-item.active {
  border-color: var(--accent);
  background: linear-gradient(180deg, #ffffff 0%, var(--soft) 100%);
  box-shadow: inset 3px 0 0 var(--accent);
}

.exercise-card {
  display: grid;
  grid-template-columns: minmax(0, 1fr) auto;
  gap: 16px;
  align-items: center;
}

.practice-button {
  border: 0;
  cursor: pointer;
}

.practice-button:disabled {
  cursor: not-allowed;
  opacity: 0.55;
}

.practice-start-card {
  display: grid;
  grid-template-columns: minmax(0, 1fr) auto;
  gap: 16px;
  align-items: center;
  border: 1px solid var(--line);
  border-radius: 12px;
  background: var(--panel);
  padding: 20px;
  box-shadow: var(--shadow);
}

.practice-start-card h3 {
  margin: 8px 0;
}

.practice-start-card p {
  margin: 0;
  color: var(--muted);
  line-height: 1.7;
}

.practice-layout {
  display: grid;
  grid-template-columns: 230px minmax(0, 1fr);
  gap: 16px;
  align-items: start;
}

.question-nav {
  display: grid;
  gap: 8px;
  position: sticky;
  top: 18px;
}

.question-dot {
  display: flex;
  justify-content: space-between;
  gap: 10px;
  align-items: center;
  min-height: 42px;
  border: 1px solid var(--line);
  border-radius: 10px;
  background: var(--panel);
  color: var(--ink);
  cursor: pointer;
  padding: 8px 10px;
  text-align: left;
}

.question-dot span {
  display: grid;
  width: 26px;
  height: 26px;
  place-items: center;
  border-radius: 8px;
  background: #e8edf6;
  font-weight: 800;
}

.question-dot small {
  color: var(--muted);
  font-weight: 700;
}

.question-dot.done span {
  background: var(--soft);
  color: var(--accent-dark);
}

.question-dot.active {
  border-color: var(--accent);
  box-shadow: inset 3px 0 0 var(--accent);
}

.question-paper,
.answer-card {
  border: 1px solid var(--line);
  border-radius: 12px;
  background: var(--panel);
  padding: 18px;
  box-shadow: var(--shadow);
}

.paper-head,
.paper-actions,
.answer-card-head {
  display: flex;
  justify-content: space-between;
  gap: 12px;
  align-items: center;
}

.paper-head {
  padding-bottom: 14px;
  border-bottom: 1px solid var(--line);
}

.paper-actions {
  margin-top: 18px;
}

#questionBody h2,
.answer-card h2 {
  margin: 18px 0 12px;
  font-size: 24px;
}

.question-task,
.problem-section p,
.answer-card p {
  color: var(--muted);
  line-height: 1.7;
}

.problem-section {
  margin: 14px 0;
}

.problem-section h3,
.answer-compare h3 {
  margin: 0 0 8px;
}

.sample-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 12px;
  margin: 12px 0;
}

.sample-grid > div,
.answer-compare section {
  border: 1px solid var(--line);
  border-radius: 12px;
  background: #f8fafc;
  padding: 12px;
}

.sample-grid pre,
.answer-compare pre {
  margin: 8px 0 0;
  white-space: pre-wrap;
  font: 14px/1.55 Consolas, "Courier New", monospace;
}

.answer-label {
  display: block;
  margin: 16px 0 8px;
  font-weight: 800;
}

.program-answer {
  width: 100%;
  min-height: 280px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: #151821;
  color: #edf2ff;
  padding: 14px;
  resize: vertical;
  font: 15px/1.6 Consolas, "Courier New", monospace;
}

.practice-compiler {
  display: grid;
  grid-template-columns: minmax(360px, 1fr) 320px;
  gap: 14px;
  margin-top: 16px;
}

.compiler-main,
.compiler-side {
  min-width: 0;
  border: 1px solid var(--line);
  border-radius: 12px;
  background: #f8fafc;
  overflow: hidden;
  box-shadow: 0 10px 26px rgba(24, 32, 51, 0.05);
}

.compiler-head {
  display: flex;
  justify-content: space-between;
  gap: 12px;
  align-items: center;
  min-height: 48px;
  padding: 8px 12px;
  border-bottom: 1px solid var(--line);
  background: var(--panel);
}

.program-code-input {
  width: 100%;
  min-height: 420px;
  border: 0;
  outline: 0;
  background:
    linear-gradient(180deg, rgba(255, 255, 255, 0.02), transparent),
    #151821;
  color: #edf2ff;
  padding: 14px;
  resize: vertical;
  tab-size: 2;
  font: 15px/1.6 Consolas, "Courier New", monospace;
}

.compiler-side {
  display: grid;
  grid-template-rows: auto minmax(180px, 1fr);
}

.compiler-side label,
.compiler-side > div {
  display: grid;
  gap: 8px;
  padding: 12px;
}

.compiler-side label {
  border-bottom: 1px solid var(--line);
}

.program-stdin {
  width: 100%;
  min-height: 120px;
  border: 1px solid var(--line);
  border-radius: 10px;
  background: var(--panel);
  color: var(--ink);
  padding: 10px;
  resize: vertical;
  font: 14px/1.55 Consolas, "Courier New", monospace;
}

.practice-output {
  min-height: 180px;
  margin: 0;
  border: 1px solid var(--line);
  border-radius: 10px;
  background: var(--panel);
  color: var(--ink);
  padding: 10px;
  overflow: auto;
  white-space: pre-wrap;
  font: 14px/1.55 Consolas, "Courier New", monospace;
}

.practice-output.success {
  border-color: #b9dfc8;
  background: #eef8f2;
  color: var(--success);
}

.practice-output.warning {
  border-color: #efd08e;
  background: #fff8e6;
  color: var(--warn);
}

.practice-output.error {
  border-color: #f0a1a1;
  background: #fff5f5;
  color: var(--danger);
}

.option-row {
  display: flex;
  gap: 10px;
  align-items: center;
  min-height: 44px;
  border: 1px solid var(--line);
  border-radius: 10px;
  background: #f8fafc;
  padding: 10px 12px;
  cursor: pointer;
  font-weight: 700;
}

.option-row input {
  width: 18px;
  height: 18px;
  accent-color: var(--accent);
}

.option-row:hover {
  border-color: var(--accent);
  background: #ffffff;
}

.answer-list {
  display: grid;
  gap: 14px;
}

.answer-compare {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 12px;
}

.success-tag {
  background: #e6f4ec;
  color: var(--success);
}

.danger-tag {
  background: #fdecec;
  color: var(--danger);
}

.quiz-options {
  display: grid;
  gap: 8px;
}

.option-button {
  min-height: 40px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: #f8fafc;
  color: var(--ink);
  cursor: pointer;
  font: inherit;
  font-weight: 700;
  text-align: left;
  padding: 9px 11px;
}

.option-button:hover:not(:disabled) {
  border-color: var(--accent);
  background: var(--soft);
}

.option-button.correct {
  border-color: var(--success);
  background: #e6f4ec;
  color: var(--success);
}

.option-button.wrong {
  border-color: var(--danger);
  background: #fdecec;
  color: var(--danger);
}

.answer-panel {
  margin-top: 10px;
  padding: 11px 12px;
  border-radius: 8px;
  line-height: 1.6;
  font-weight: 700;
}

.answer-panel.correct {
  background: #e6f4ec;
  color: var(--success);
}

.answer-panel.wrong {
  background: #fdecec;
  color: var(--danger);
}

.diagnosis-box {
  display: grid;
  gap: 10px;
  color: var(--muted);
  line-height: 1.7;
}

.diagnosis-box p {
  margin: 0;
}

.task-board {
  display: grid;
  gap: 12px;
}

.task-card {
  display: grid;
  grid-template-columns: 42px minmax(0, 1fr);
  gap: 14px;
  align-items: start;
  border: 1px solid var(--line);
  border-radius: 12px;
  background: var(--panel);
  padding: 16px;
  box-shadow: 0 10px 24px rgba(24, 32, 51, 0.05);
}

.task-card > span {
  display: grid;
  width: 42px;
  height: 42px;
  place-items: center;
  border-radius: 10px;
  background: var(--soft);
  color: var(--accent-dark);
  font-weight: 800;
}

.task-card h3 {
  margin: 0 0 6px;
}

.task-card p {
  margin: 0;
  color: var(--muted);
  line-height: 1.65;
}

.task-card small {
  display: inline-flex;
  margin-top: 10px;
  min-height: 26px;
  align-items: center;
  border-radius: 999px;
  background: #e8edf6;
  padding: 0 8px;
  color: var(--ink);
  font-weight: 800;
}

@media (max-width: 980px) {
  .layout {
    grid-template-columns: 1fr;
  }

  .side {
    padding: 16px;
  }

  .nav {
    grid-template-columns: repeat(3, minmax(0, 1fr));
  }

  .grid,
  .grid.two {
    grid-template-columns: 1fr;
  }

  .course-card,
  .exercise-card,
  .practice-start-card,
  .practice-layout,
  .practice-compiler,
  .video-course,
  .sample-grid,
  .answer-compare {
    grid-template-columns: 1fr;
  }

  .course-actions {
    justify-content: flex-start;
  }
}

@media (max-width: 640px) {
  .main {
    padding: 18px;
  }

  .topbar {
    flex-direction: column;
  }

  .nav {
    grid-template-columns: 1fr;
  }

  h1 {
    font-size: 28px;
  }

  .slide-body {
    padding: 18px;
  }

  .slide-body h3 {
    font-size: 24px;
  }

  .video-visual {
    grid-template-columns: 1fr;
  }

  .video-visual h3 {
    font-size: 24px;
  }
}