:root {
  color-scheme: light;
  --bg: #f4f7f7;
  --surface: #ffffff;
  --surface-soft: #edf6f5;
  --surface-warm: #fff8ed;
  --line: #d8e2e2;
  --line-strong: #bdcece;
  --text: #17272d;
  --text-soft: #52666d;
  --accent: #0f766e;
  --accent-strong: #0b5e58;
  --accent-pale: #dff2ef;
  --warning: #a85b11;
  --warning-pale: #fff1dc;
  --danger: #a13d35;
  --danger-pale: #fff0ee;
  --shadow: 0 12px 30px rgba(26, 53, 57, 0.08);
  font-family: "Microsoft YaHei UI", "Microsoft YaHei", "PingFang SC", system-ui, sans-serif;
}

* {
  box-sizing: border-box;
}

html {
  min-width: 320px;
  background: var(--bg);
}

body {
  margin: 0;
  min-width: 320px;
  color: var(--text);
  background: var(--bg);
  line-height: 1.65;
  letter-spacing: 0;
}

button,
select,
input {
  font: inherit;
}

button,
summary,
select {
  cursor: pointer;
}

button:focus-visible,
select:focus-visible,
input:focus-visible,
summary:focus-visible,
a:focus-visible {
  outline: 3px solid rgba(15, 118, 110, 0.22);
  outline-offset: 2px;
}

[hidden] {
  display: none !important;
}

.app-header {
  position: sticky;
  top: 0;
  z-index: 20;
  border-bottom: 1px solid var(--line);
  background: rgba(255, 255, 255, 0.96);
  backdrop-filter: blur(12px);
}

.header-inner {
  width: min(1280px, calc(100% - 40px));
  min-height: 70px;
  margin: 0 auto;
  display: grid;
  grid-template-columns: auto 1fr auto;
  align-items: center;
  gap: 28px;
}

.brand {
  border: 0;
  padding: 0;
  display: inline-flex;
  align-items: center;
  gap: 12px;
  color: var(--text);
  background: transparent;
  text-align: left;
}

.brand-mark {
  width: 44px;
  height: 44px;
  display: grid;
  place-items: center;
  border-radius: 8px;
  color: #fff;
  background: var(--accent);
  font-size: 14px;
  font-weight: 800;
}

.brand-copy {
  display: grid;
  line-height: 1.25;
}

.brand-copy strong {
  font-size: 16px;
}

.brand-copy small {
  margin-top: 4px;
  color: var(--text-soft);
  font-size: 12px;
}

.main-nav {
  justify-self: center;
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 4px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: #f6f9f9;
}

.nav-button {
  min-height: 36px;
  padding: 0 16px;
  border: 0;
  border-radius: 6px;
  color: var(--text-soft);
  background: transparent;
  font-weight: 700;
}

.nav-button.is-active {
  color: var(--accent-strong);
  background: var(--surface);
  box-shadow: 0 2px 8px rgba(31, 68, 70, 0.08);
}

.total-badge {
  min-width: 58px;
  padding: 6px 10px;
  border: 1px solid #b7dcd7;
  border-radius: 6px;
  color: var(--accent-strong);
  background: var(--accent-pale);
  text-align: center;
  font-size: 13px;
  font-weight: 800;
}

.overview-view {
  width: min(1180px, calc(100% - 40px));
  margin: 34px auto 64px;
}

.overview-intro {
  padding: 34px 38px;
  border: 1px solid var(--line);
  border-left: 6px solid var(--accent);
  border-radius: 8px;
  background: var(--surface);
  box-shadow: var(--shadow);
}

.eyebrow {
  margin: 0 0 8px;
  color: var(--accent);
  font-size: 13px;
  font-weight: 800;
}

.overview-intro h1 {
  max-width: 820px;
  margin: 0;
  font-size: clamp(30px, 4vw, 50px);
  line-height: 1.16;
}

.overview-intro > p:not(.eyebrow) {
  max-width: 820px;
  margin: 18px 0 0;
  color: var(--text-soft);
  font-size: 16px;
}

.overview-stats {
  margin-top: 28px;
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
}

.overview-stats span {
  min-width: 118px;
  padding: 10px 14px;
  border: 1px solid var(--line);
  border-radius: 6px;
  background: #f8fbfb;
  color: var(--text-soft);
}

.overview-stats strong {
  margin-right: 4px;
  color: var(--accent-strong);
  font-size: 22px;
}

.path-section,
.modules-section {
  margin-top: 42px;
}

.section-heading {
  margin-bottom: 16px;
}

.section-heading h2 {
  margin: 0;
  font-size: 25px;
}

.knowledge-path {
  counter-reset: path-step;
  margin: 0;
  padding: 0;
  display: grid;
  grid-template-columns: repeat(8, minmax(0, 1fr));
  border: 1px solid var(--line);
  border-radius: 8px;
  overflow: hidden;
  list-style: none;
  background: var(--surface);
}

.knowledge-path li {
  counter-increment: path-step;
  position: relative;
  min-height: 86px;
  padding: 40px 12px 14px;
  border-right: 1px solid var(--line);
  display: flex;
  align-items: center;
  justify-content: center;
  color: var(--text);
  text-align: center;
  font-size: 13px;
  font-weight: 700;
}

.knowledge-path li:last-child {
  border-right: 0;
}

.knowledge-path li::before {
  content: counter(path-step, decimal-leading-zero);
  position: absolute;
  top: 12px;
  left: 50%;
  transform: translateX(-50%);
  color: var(--accent);
  font-size: 12px;
  font-weight: 800;
}

.module-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 14px;
}

.module-card {
  min-width: 0;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--surface);
  overflow: clip;
}

.module-card[open] {
  border-color: #b9d7d3;
  box-shadow: 0 8px 22px rgba(26, 68, 69, 0.07);
}

.module-card summary {
  min-height: 66px;
  padding: 14px 16px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 14px;
  list-style: none;
  user-select: none;
}

.module-card summary::-webkit-details-marker {
  display: none;
}

.module-card summary::after {
  content: "+";
  flex: 0 0 auto;
  width: 24px;
  color: var(--accent);
  text-align: center;
  font-size: 20px;
  font-weight: 700;
}

.module-card[open] summary::after {
  content: "−";
}

.module-title-wrap {
  min-width: 0;
  display: flex;
  align-items: center;
  gap: 12px;
}

.module-number {
  color: var(--accent);
  font-size: 12px;
  font-weight: 800;
}

.module-title {
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
  font-weight: 800;
}

.module-count {
  margin-left: auto;
  color: var(--text-soft);
  font-size: 12px;
  font-weight: 700;
}

.module-body {
  padding: 0 16px 18px;
  border-top: 1px solid var(--line);
}

.module-focus {
  margin: 14px 0;
  color: var(--text-soft);
  font-size: 13px;
}

.module-start {
  min-height: 38px;
  padding: 0 14px;
  border: 1px solid var(--accent);
  border-radius: 6px;
  color: #fff;
  background: var(--accent);
  font-weight: 700;
}

.module-start:hover {
  background: var(--accent-strong);
}

.question-directory {
  margin: 16px 0 0;
  padding: 0 0 0 24px;
  max-height: 310px;
  overflow: auto;
  border-top: 1px dashed var(--line);
}

.question-directory li {
  padding: 10px 4px;
  border-bottom: 1px solid #edf1f1;
  color: var(--text-soft);
  font-size: 13px;
}

.question-directory button {
  width: 100%;
  padding: 0;
  border: 0;
  color: var(--text);
  background: transparent;
  text-align: left;
  line-height: 1.55;
}

.question-directory button:hover {
  color: var(--accent);
}

.source-section {
  margin-top: 36px;
  border-top: 1px solid var(--line);
  border-bottom: 1px solid var(--line);
  background: transparent;
}

.source-section summary {
  padding: 16px 0;
  color: var(--text);
  font-weight: 800;
}

.source-list {
  padding-bottom: 20px;
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 10px 22px;
}

.source-list a {
  min-width: 0;
  padding: 11px 0;
  display: grid;
  border-bottom: 1px solid #e4ebeb;
  color: var(--text);
  text-decoration: none;
}

.source-list a:hover strong {
  color: var(--accent);
}

.source-list strong {
  font-size: 13px;
}

.source-list span {
  margin-top: 3px;
  color: var(--text-soft);
  font-size: 12px;
}

.drill-view {
  width: min(1280px, calc(100% - 40px));
  margin: 28px auto 64px;
}

.drill-shell {
  display: grid;
  grid-template-columns: 250px minmax(0, 1fr);
  align-items: start;
  gap: 22px;
}

.module-rail {
  position: sticky;
  top: 94px;
  max-height: calc(100vh - 116px);
  overflow: auto;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--surface);
}

.rail-title {
  padding: 14px 14px 12px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  border-bottom: 1px solid var(--line);
  color: var(--text-soft);
  font-size: 12px;
}

.rail-title strong {
  color: var(--accent);
}

.rail-modules {
  padding: 6px;
}

.rail-modules button {
  width: 100%;
  min-height: 42px;
  padding: 8px 10px;
  border: 0;
  border-radius: 6px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 10px;
  color: var(--text-soft);
  background: transparent;
  text-align: left;
  font-size: 13px;
}

.rail-modules button:hover {
  color: var(--accent-strong);
  background: #f2f7f6;
}

.rail-modules button.is-active {
  color: var(--accent-strong);
  background: var(--accent-pale);
  font-weight: 800;
}

.rail-modules small {
  flex: 0 0 auto;
  color: inherit;
  font-size: 11px;
}

.drill-content {
  min-width: 0;
}

.drill-toolbar {
  min-height: 62px;
  padding: 10px 12px;
  border: 1px solid var(--line);
  border-radius: 8px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 14px;
  background: var(--surface);
}

.mode-control {
  display: inline-flex;
  padding: 3px;
  border: 1px solid var(--line);
  border-radius: 7px;
  background: #f5f8f8;
}

.mode-button {
  min-height: 34px;
  padding: 0 14px;
  border: 0;
  border-radius: 5px;
  color: var(--text-soft);
  background: transparent;
  font-weight: 700;
}

.mode-button.is-active {
  color: #fff;
  background: var(--accent);
}

.mobile-module-field,
.jump-field {
  display: flex;
  align-items: center;
  gap: 8px;
  color: var(--text-soft);
  font-size: 12px;
  font-weight: 700;
}

.mobile-module-field {
  display: none;
}

.mobile-module-field select,
.jump-field input,
.jump-field button {
  min-height: 36px;
  border: 1px solid var(--line-strong);
  border-radius: 6px;
  color: var(--text);
  background: #fff;
}

.mobile-module-field select {
  max-width: 230px;
  padding: 0 32px 0 10px;
}

.jump-field input {
  width: 68px;
  padding: 0 8px;
}

.jump-field button {
  padding: 0 11px;
  font-weight: 700;
}

.progress-block {
  margin-top: 14px;
}

.progress-copy {
  margin-bottom: 7px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 14px;
  color: var(--text-soft);
  font-size: 12px;
}

.progress-copy strong {
  color: var(--text);
}

.progress-track {
  height: 5px;
  overflow: hidden;
  border-radius: 3px;
  background: #dce7e6;
}

.progress-track span {
  display: block;
  width: 0;
  height: 100%;
  background: var(--accent);
  transition: width 180ms ease;
}

.question-card {
  margin-top: 14px;
  padding: clamp(24px, 4vw, 44px);
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--surface);
  box-shadow: var(--shadow);
}

.question-meta {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 8px;
}

.tag {
  padding: 5px 9px;
  border: 1px solid #b6dcd7;
  border-radius: 5px;
  color: var(--accent-strong);
  background: var(--accent-pale);
  font-size: 12px;
  font-weight: 800;
}

.tag.quiet {
  border-color: var(--line);
  color: var(--text-soft);
  background: #f5f8f8;
}

.question-id {
  margin-left: auto;
  color: #829398;
  font-family: Consolas, monospace;
  font-size: 12px;
}

.question-card > h1 {
  max-width: 900px;
  margin: 24px 0 30px;
  font-size: clamp(25px, 3.3vw, 38px);
  line-height: 1.36;
}

.answer-panel {
  margin: 0 0 28px;
  border-top: 4px solid var(--accent);
  background: #fbfdfd;
}

.answer-section {
  padding: 22px 24px;
  border-right: 1px solid var(--line);
  border-bottom: 1px solid var(--line);
  border-left: 1px solid var(--line);
}

.answer-main {
  background: var(--surface-soft);
}

.answer-section h2 {
  margin: 0 0 11px;
  color: var(--accent-strong);
  font-size: 15px;
}

.answer-section p {
  margin: 0;
  color: var(--text);
  font-size: 16px;
  line-height: 1.85;
}

.answer-points {
  margin: 0;
  padding-left: 22px;
}

.answer-points li {
  margin: 7px 0;
  padding-left: 3px;
}

.answer-points li::marker {
  color: var(--accent);
  font-weight: 800;
}

.answer-callout {
  padding: 18px 24px;
  border-right: 1px solid var(--line);
  border-bottom: 1px solid var(--line);
  border-left: 4px solid var(--accent);
  background: #fff;
}

.answer-callout span {
  display: block;
  margin-bottom: 5px;
  color: var(--accent-strong);
  font-size: 12px;
  font-weight: 800;
}

.answer-callout p {
  margin: 0;
}

.example-callout {
  border-left-color: var(--warning);
  background: var(--surface-warm);
}

.example-callout span {
  color: var(--warning);
}

.pitfall-callout {
  border-left-color: var(--danger);
  background: var(--danger-pale);
}

.pitfall-callout span {
  color: var(--danger);
}

.follow-hint {
  margin: -2px 0 14px !important;
  color: var(--text-soft) !important;
  font-size: 13px !important;
}

.follow-list {
  display: grid;
  gap: 10px;
}

.follow-card {
  overflow: hidden;
  border: 1px solid var(--line);
  border-radius: 7px;
  background: var(--surface);
}

.follow-card summary {
  min-height: 56px;
  padding: 11px 14px;
  display: grid;
  grid-template-columns: 34px 1fr auto;
  gap: 10px;
  align-items: center;
  cursor: pointer;
  list-style: none;
}

.follow-card summary::-webkit-details-marker {
  display: none;
}

.follow-card summary:hover {
  background: var(--surface-soft);
}

.follow-number {
  color: var(--accent);
  font-size: 12px;
  font-weight: 800;
}

.follow-card summary strong {
  color: var(--text);
  font-size: 15px;
  line-height: 1.55;
}

.follow-toggle-label {
  color: var(--accent);
  font-size: 12px;
  white-space: nowrap;
}

.follow-card[open] .follow-toggle-label {
  font-size: 0;
}

.follow-card[open] .follow-toggle-label::after {
  content: "收起回答";
  font-size: 12px;
}

.follow-body {
  padding: 16px 18px 18px 58px;
  border-top: 1px solid var(--line);
  background: #fbfdfd;
}

.follow-answer-label,
.follow-decision > span {
  display: block;
  margin-bottom: 6px;
  color: var(--accent-strong);
  font-size: 12px;
  font-weight: 800;
}

.follow-body > p,
.follow-decision p {
  margin: 0;
  color: var(--text);
  font-size: 15px;
  line-height: 1.8;
}

.follow-decision {
  margin-top: 14px;
  padding: 12px 14px;
  border-left: 3px solid var(--accent);
  background: var(--surface-soft);
}

.source-answer-section {
  background: #f8fbfb;
}

.answer-sources {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
}

.answer-sources a {
  padding: 5px 9px;
  border: 1px solid var(--line-strong);
  border-radius: 5px;
  color: var(--text-soft);
  background: #fff;
  text-decoration: none;
  font-size: 12px;
}

.answer-sources a:hover {
  color: var(--accent);
  border-color: #9acbc5;
}

.primary-actions {
  display: grid;
  grid-template-columns: 1fr minmax(150px, 1.3fr) 1fr;
  gap: 10px;
}

.button,
.random-button {
  min-height: 48px;
  border-radius: 7px;
  font-weight: 800;
}

.button {
  padding: 0 18px;
  border: 1px solid var(--line-strong);
}

.button.primary {
  color: #fff;
  border-color: var(--accent);
  background: var(--accent);
}

.button.primary:hover {
  background: var(--accent-strong);
}

.button.secondary {
  color: var(--text);
  background: #fff;
}

.button.secondary:hover {
  color: var(--accent);
  border-color: #9acbc5;
}

.random-button {
  width: 100%;
  margin-top: 10px;
  border: 1px dashed var(--line-strong);
  color: var(--text-soft);
  background: #f8fbfb;
}

.random-button:hover {
  color: var(--accent);
  border-color: var(--accent);
}

@media (max-width: 960px) {
  .knowledge-path {
    grid-template-columns: repeat(4, minmax(0, 1fr));
  }

  .knowledge-path li:nth-child(4) {
    border-right: 0;
  }

  .knowledge-path li:nth-child(-n + 4) {
    border-bottom: 1px solid var(--line);
  }

  .drill-shell {
    grid-template-columns: 1fr;
  }

  .module-rail {
    display: none;
  }

  .mobile-module-field {
    display: flex;
  }
}

@media (max-width: 740px) {
  .header-inner {
    width: min(100% - 24px, 680px);
    min-height: 62px;
    grid-template-columns: 1fr auto;
    gap: 10px;
  }

  .brand-mark {
    width: 38px;
    height: 38px;
    font-size: 12px;
  }

  .brand-copy strong {
    font-size: 14px;
  }

  .brand-copy small,
  .total-badge {
    display: none;
  }

  .main-nav {
    justify-self: end;
  }

  .nav-button {
    min-height: 34px;
    padding: 0 10px;
    font-size: 12px;
  }

  .overview-view,
  .drill-view {
    width: calc(100% - 24px);
    margin-top: 20px;
  }

  .overview-intro {
    padding: 25px 22px;
  }

  .overview-intro h1 {
    font-size: 32px;
  }

  .overview-intro > p:not(.eyebrow) {
    font-size: 14px;
  }

  .overview-stats span {
    flex: 1 1 100px;
    min-width: 0;
  }

  .module-grid,
  .source-list {
    grid-template-columns: 1fr;
  }

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

  .knowledge-path li,
  .knowledge-path li:nth-child(4) {
    border-right: 1px solid var(--line);
    border-bottom: 1px solid var(--line);
  }

  .knowledge-path li:nth-child(2n) {
    border-right: 0;
  }

  .knowledge-path li:nth-last-child(-n + 2) {
    border-bottom: 0;
  }

  .drill-toolbar {
    align-items: stretch;
    flex-direction: column;
  }

  .mode-control {
    display: grid;
    grid-template-columns: 1fr 1fr;
  }

  .mobile-module-field,
  .jump-field {
    width: 100%;
  }

  .mobile-module-field select {
    min-width: 0;
    max-width: none;
    flex: 1;
  }

  .jump-field input {
    flex: 1;
  }

  .question-card {
    padding: 22px 18px;
  }

  .question-card > h1 {
    margin: 20px 0 24px;
    font-size: 27px;
  }

  .answer-section,
  .answer-callout {
    padding: 18px 16px;
  }

  .answer-section p {
    font-size: 15px;
  }

  .primary-actions {
    grid-template-columns: 1fr 1fr;
  }

  .button.primary {
    grid-column: 1 / -1;
    grid-row: 1;
  }

  .button.primary[hidden] + .button.secondary {
    grid-column: auto;
  }
}

@media (max-width: 420px) {
  .brand-copy small {
    display: none;
  }

  .overview-intro h1 {
    font-size: 28px;
  }

  .question-card > h1 {
    font-size: 24px;
  }

  .module-title {
    white-space: normal;
  }
}

@media (prefers-reduced-motion: reduce) {
  * {
    scroll-behavior: auto !important;
    transition: none !important;
  }
}