/* 练习册风格：浅纸色、墨绿色和清晰数字。所有资源使用本地文件，不依赖外部字体。 */
:root {
  color-scheme: light;
  --paper: #f7f5ed;
  --surface: #fffef9;
  --ink: #233c34;
  --green: #204e40;
  --muted: #778078;
  --line: #dce1d6;
  --mint: #e8eedf;
  --orange: #b8663d;
  --red: #af4435;
  --serif: Georgia,"Songti SC","STSong","SimSun",serif;
  --sans: "PingFang SC","Microsoft YaHei","Noto Sans CJK SC",sans-serif;
  --numbers: "Cambria Math",Cambria,Georgia,serif;
  font-family: var(--sans);
  background: var(--paper);
  color: var(--ink);
  font-synthesis: none;
}
* {
  box-sizing: border-box;
}
body {
  margin: 0;
  min-width: 320px;
}
button,a,input,summary {
  -webkit-tap-highlight-color:transparent
}
button,input {
  font: inherit;
}
button,a,summary {
  touch-action: manipulation;
}
button {
  cursor: pointer;
}
button:disabled {
  cursor: default;
  opacity: .4;
}
a {
  color: inherit;
  text-decoration: none;
}
button:focus-visible,a:focus-visible,input:focus-visible,summary:focus-visible {
  outline: 3px solid #b8663d;
  outline-offset: 4px;
}
button {
  color: inherit;
}
h1,h2,h3,p {
  margin: 0;
}
h1,h2,h3 {
  font-weight: 500;
}
button {
  border: 0;
}
button:disabled:hover {
  transform: none;
}
main:focus {
  outline: none;
}
/* 页头和品牌区：共享桌面与手机导航，切换语言不离开当前练习。 */
.site-header {
  max-width: 1104px;
  padding: 24px 28px;
  margin: auto;
  display: flex;
  align-items: center;
  justify-content: space-between;
  border-bottom: 1px solid var(--line);
}
.brand {
  display: flex;
  align-items: center;
  gap: 11px;
  font-weight: 700;
  letter-spacing: .05em;
}
.brand-symbol {
  display: grid;
  place-items: center;
  background: var(--green);
  color: var(--paper);
  width: 35px;
  height: 35px;
  border-radius: 11px;
  font: 30px/1 var(--numbers);
}
.language-button {
  background: none;
  color: var(--muted);
  padding: 12px 0 12px 18px;
  font-size: 12px;
  letter-spacing: .1em;
}
.language-button span {
  margin-left: 8px;
}
main {
  max-width: 1104px;
  margin: auto;
  padding: 0 28px;
}
.site-footer {
  text-align: center;
  color: var(--muted);
  font-size: 11px;
  letter-spacing: .12em;
  padding: 34px 20px calc(28px + env(safe-area-inset-bottom));
  line-height: 1.6;
}
.eyebrow {
  font-size: 10px;
  font-weight: 700;
  letter-spacing: .18em;
  color: var(--muted);
  line-height: 1.7;
}
.button {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 12px;
  border-radius: 11px;
  min-height: 48px;
  padding: 12px 20px;
  font-size: 13px;
  font-weight: 600;
  transition: background .15s,transform .15s;
  line-height: 1.4;
}
.button.primary {
  background: var(--green);
  color: #fffef9;
}
.button.primary:hover {
  background: #173e32;
}
.button.secondary {
  border: 1px solid var(--line);
  background: transparent;
}
.button.secondary:hover {
  background: var(--mint);
}
.button.wide {
  width: 100%;
}
.arrow {
  font-size: 22px;
  font-weight: 400;
}
.continue-card {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 15px;
  background: var(--green);
  border-radius: 15px;
  padding: 19px 22px;
  color: var(--paper);
  margin-bottom: 22px;
}
.continue-card h2 {
  font-size: 13px;
  margin-bottom: 7px;
}
.continue-card p {
  font-size: 11px;
  color: #c6d4c8;
  line-height: 1.6;
}
.continue-card .button {
  background: #f7f5ed;
  color: var(--green);
  flex-shrink: 0;
  min-height: 42px;
  font-size: 12px;
}
/* 单题练习区：只读输入框配合页面数字键盘，避免系统键盘改变布局。 */
.session-wrap {
  max-width: 670px;
  margin: 30px auto 0;
}
.session-toolbar {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 8px;
  margin-bottom: 25px;
}
.text-button {
  background: none;
  padding: 10px 0;
  color: var(--muted);
  font-size: 12px;
  display: inline-flex;
  align-items: center;
  gap: 7px;
}
.session-type {
  font-size: 11px;
  color: var(--muted);
  text-align: right;
}
.progress-meta {
  display: flex;
  justify-content: space-between;
  align-items: center;
  font-size: 12px;
  margin-bottom: 12px;
}
.timer {
  font: 18px var(--numbers);
  font-variant-numeric: tabular-nums;
}
.timer small {
  font: 10px var(--sans);
  color: var(--muted);
  margin-right: 10px;
}
.progress-track {
  height: 3px;
  background: var(--line);
  border-radius: 3px;
  overflow: hidden;
}
.progress-track span {
  display: block;
  height: 100%;
  background: var(--green);
  transition: width .2s;
}
.question-panel {
  padding: 39px 32px 24px;
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: 22px;
  margin-top: 23px;
  text-align: center;
}
.question-label {
  font-size: 10px;
  letter-spacing: .1em;
  color: var(--muted);
}
.equation {
  font: clamp(33px,7vw,52px)/1.2 var(--numbers);
  letter-spacing: .01em;
  white-space: nowrap;
  color: var(--green);
  margin: 20px 0 14px;
}
.question-hint {
  font-size: 11px;
  color: var(--muted);
  line-height: 1.6;
  min-height: 18px;
}
.answer-input {
  display: block;
  margin: 25px auto 8px;
  width: 100%;
  height: 58px;
  border: 1px solid var(--line);
  border-radius: 12px;
  background: var(--paper);
  text-align: center;
  color: var(--ink);
  font: 31px var(--numbers);
  caret-color: transparent;
}
.answer-input::placeholder {
  font: 13px var(--sans);
  color: #97a091;
}
.answer-input:focus {
  outline: 2px solid var(--green);
  outline-offset: 1px;
}
.keypad {
  display: grid;
  grid-template-columns: repeat(3,minmax(0,1fr));
  gap: 8px;
  margin-top: 15px;
}
.key {
  min-height: 53px;
  background: #f0f2e9;
  border: 1px solid transparent;
  border-radius: 11px;
  font: 24px var(--numbers);
  color: var(--ink);
  user-select: none;
}
.key:hover {
  background: #e5eadc;
}
.key:active {
  background: #d2ddc7;
  transform: translateY(1px);
}
.key.function {
  font: 21px var(--sans);
  background: transparent;
  border-color: var(--line);
}
/* 单题确认后显示反馈并锁定输入，反馈区保持键盘原高度，避免下一题按钮跳动。 */
.answer-feedback {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 13px;
  min-height: 236px;
  margin-top: 15px;
  padding: 20px 15px;
  border: 1px solid #cddcc6;
  border-radius: 12px;
  background: #edf2e6;
}
.answer-feedback.is-incorrect {
  border-color: #ead9cb;
  background: #faf0e6;
}
.feedback-marker {
  display: grid;
  place-items: center;
  width: 40px;
  height: 40px;
  border-radius: 50%;
  background: #dae6d1;
  color: var(--green);
  font: 27px var(--sans);
}
.is-incorrect .feedback-marker {
  background: #eedbcc;
  color: var(--orange);
}
.answer-feedback h2 {
  font: 23px var(--serif);
}
.answer-feedback p {
  color: var(--muted);
  font-size: 12px;
}
.answer-feedback strong {
  margin-left: 10px;
  font: 25px var(--numbers);
  color: var(--green);
}
.feedback-note {
  font-size: 10px;
  color: var(--muted);
}
.jump-button.incorrect {
  border-color: #d5b5a4;
  color: var(--red);
  background: #f5e6dc;
}
.session-bottom-actions {
  display: flex;
  justify-content: center;
  gap: 25px;
}
@media (max-width: 700px) {
  .answer-feedback {
    min-height: 213px;
    margin-top: 12px;
  }
}
.session-navigation {
  display: grid;
  grid-template-columns: 1fr 1.55fr;
  gap: 12px;
  margin-top: 15px;
}
.question-jumps {
  display: flex;
  gap: 7px;
  flex-wrap: wrap;
  margin: 21px 0 13px;
  justify-content: center;
}
.jump-button {
  height: 29px;
  min-width: 29px;
  border: 1px solid var(--line);
  border-radius: 7px;
  font: 11px var(--numbers);
  background: transparent;
  color: var(--muted);
}
.jump-button.filled {
  background: var(--mint);
  color: var(--green);
}
.jump-button.current {
  border-color: var(--green);
  box-shadow: inset 0 0 0 .5px var(--green);
  color: var(--green);
}
.answered-caption {
  text-align: center;
  color: var(--muted);
  font-size: 10px;
}
.pause-panel {
  background: var(--surface);
  padding: 55px 26px;
  border: 1px solid var(--line);
  border-radius: 22px;
  margin-top: 23px;
  text-align: center;
}
.pause-icon {
  font: 50px var(--numbers);
  color: var(--green);
  margin-bottom: 20px;
}
.pause-panel h1 {
  font: 27px/1.5 var(--serif);
}
.pause-panel p {
  font-size: 12px;
  line-height: 1.9;
  color: var(--muted);
  margin: 15px 0 25px;
}
/* 本组成绩与练习记录使用清晰的数字层级，手机端保持单列阅读。 */
.result-wrap {
  max-width: 730px;
  margin: 36px auto 0;
}
/* 汇总页及记录页只展示统计数据，不提供题目回看和错题入口。 */
.result-card .score-main strong {
  font-size: clamp(38px, 11vw, 64px);
}
.records-wrap {
  max-width: 670px;
  margin: 30px auto 0;
}
.records-heading {
  margin: 22px 0 25px;
}
.records-heading h1 {
  font: 31px/1.4 var(--serif);
}
.records-heading p {
  margin-top: 9px;
  color: var(--muted);
  font-size: 12px;
}
.record-row {
  padding: 20px;
  margin-bottom: 13px;
  border: 1px solid var(--line);
  border-radius: 15px;
  background: var(--surface);
}
.record-top {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 15px;
  padding-bottom: 17px;
  border-bottom: 1px solid var(--line);
}
.record-number {
  flex-shrink: 0;
  color: var(--muted);
  font-size: 11px;
}
.record-top dl {
  display: flex;
  align-items: center;
  justify-content: flex-end;
  gap: 11px;
  margin: 0;
}
.record-row dt {
  color: var(--muted);
  font-size: 10px;
}
.record-row dd {
  margin: 0;
}
.record-top dd {
  font-size: 12px;
  line-height: 1.6;
}
.record-stats {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 12px;
  margin: 18px 0 0;
}
.record-stats dd {
  margin-top: 8px;
  color: var(--green);
  font: 22px/1.3 var(--numbers);
}
.records-empty {
  padding: 40px 25px;
  border: 1px dashed var(--line);
  border-radius: 15px;
  color: var(--muted);
  text-align: center;
  font-size: 12px;
  line-height: 1.9;
}
@media (max-width: 700px) {
  .records-wrap {
    margin-top: 15px;
  }
  .record-row {
    padding: 17px;
  }
  .record-stats dd {
    font-size: 20px;
  }
}
.result-heading {
  text-align: center;
  margin: 27px 0;
}
.result-heading h1 {
  font: 33px/1.4 var(--serif);
  margin-top: 13px;
}
.result-card {
  background: var(--green);
  color: var(--paper);
  border-radius: 23px;
  padding: 31px;
  display: grid;
  grid-template-columns: 1fr 1fr;
  align-items: center;
  gap: 25px;
}
.score-main {
  border-right: 1px solid #557566;
  padding-right: 20px;
}
.score-main .eyebrow {
  color: #bdcdbb;
}
.score-main strong {
  font: 72px/1.2 var(--numbers);
  display: block;
  margin: 5px 0;
}
.score-main strong span {
  font-size: 30px;
  margin-left: 4px;
}
.score-main p {
  font-size: 12px;
  color: #c5d3c6;
}
.time-stats {
  display: grid;
  gap: 22px;
}
.time-stats dt {
  font-size: 11px;
  color: #c5d3c6;
  margin-bottom: 6px;
}
.time-stats dd {
  font: 27px var(--numbers);
  margin: 0;
}
.result-actions {
  display: flex;
  gap: 10px;
  margin: 18px 0 30px;
}
.result-actions .button {
  flex: 1;
}
.loading,.fatal {
  padding: 80px 0;
  text-align: center;
  color: var(--muted);
  font-size: 13px;
  line-height: 1.9;
}
.loading-dot {
  display: block;
  width: 15px;
  height: 15px;
  border: 2px solid var(--line);
  border-top-color: var(--green);
  border-radius: 50%;
  margin: 0 auto 20px;
  animation: spin 1s linear infinite;
}
.fatal h1 {
  font: 30px var(--serif);
  color: var(--ink);
  margin-bottom: 18px;
}
.fatal p {
  max-width: 500px;
  margin: 0 auto 20px;
}
.fatal pre {
  text-align: left;
  max-width: 650px;
  margin: 20px auto;
  padding: 16px;
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: 10px;
  white-space: pre-wrap;
  overflow-wrap: anywhere;
  font-size: 11px;
  color: var(--red);
}
.notice {
  position: fixed;
  left: 50%;
  bottom: calc(22px + env(safe-area-inset-bottom));
  transform: translate(-50%,20px);
  background: var(--ink);
  color: var(--paper);
  font-size: 12px;
  line-height: 1.6;
  padding: 12px 20px;
  border-radius: 12px;
  max-width: 90%;
  width: max-content;
  opacity: 0;
  pointer-events: none;
  transition: .2s;
  z-index: 10;
}
.notice.visible {
  opacity: 1;
  transform: translate(-50%,0);
}
dialog {
  width: calc(100% - 40px);
  max-width: 410px;
  border: 1px solid var(--line);
  border-radius: 23px;
  padding: 29px;
  background: var(--surface);
  color: var(--ink);
  box-shadow: 0 20px 90px #172f3526;
}
dialog::backdrop {
  background: #172f355e;
  backdrop-filter: blur(3px);
}
.dialog-mark {
  background: var(--mint);
  width: 37px;
  height: 37px;
  border-radius: 50%;
  display: grid;
  place-items: center;
  font: 23px var(--serif);
  margin-bottom: 17px;
}
dialog h2 {
  font: 25px/1.5 var(--serif);
}
dialog p {
  font-size: 12px;
  color: var(--muted);
  line-height: 1.9;
  margin-top: 14px;
}
.dialog-actions {
  display: flex;
  gap: 9px;
  margin-top: 25px;
}
.dialog-actions .button {
  flex: 1;
  font-size: 12px;
  padding-inline: 10px;
}
.screen-enter {
  animation: enter .25s ease both;
}
@keyframes enter {
  from {
    opacity: 0;
  }
  to {
    opacity: 1;
  }
}
@keyframes spin {
  to {
    transform: rotate(360deg);
  }
}
@media(min-width:850px) {
  .session-wrap .question-panel {
    max-width: 520px;
    margin-inline: auto;
  }
  .session-wrap .question-jumps {
    max-width: 520px;
    margin-inline: auto;
  }
  .key {
    min-height: 58px;
  }
}
/* 手机主布局：单列内容、触摸按钮和安全区域适配。 */
@media(max-width:700px) {
  .site-header {
    padding: 17px 21px;
  }
  .brand {
    font-size: 14px;
  }
  .brand-symbol {
    width: 31px;
    height: 31px;
    font-size: 27px;
  }
  main {
    padding: 0 20px;
  }
  .continue-card {
    padding: 17px;
    align-items: flex-start;
  }
  .continue-card .button {
    font-size: 11px;
    padding: 10px 13px;
  }
  .continue-card p {
    font-size: 10px;
  }
  .session-wrap {
    margin-top: 15px;
  }
  .session-toolbar {
    margin-bottom: 17px;
  }
  .question-panel {
    padding: 26px 17px 20px;
    margin-top: 18px;
    border-radius: 18px;
  }
  .equation {
    font-size: clamp(30px,7.6vw,43px);
    margin: 17px 0 12px;
  }
  .answer-input {
    margin-top: 20px;
    height: 52px;
  }
  .keypad {
    gap: 7px;
    margin-top: 12px;
  }
  .key {
    min-height: 48px;
  }
  .session-navigation {
    gap: 9px;
    margin-top: 12px;
  }
  .session-navigation .button {
    min-height: 44px;
  }
  .question-jumps {
    margin-top: 17px;
    gap: 6px;
  }
  .jump-button {
    min-width: 27px;
    height: 27px;
  }
  .session-wrap+.site-footer {
    padding-top: 20px;
  }
  .result-wrap {
    margin-top: 20px;
  }
  .result-heading h1 {
    font-size: 27px;
  }
  .result-card {
    padding: 24px 20px;
    gap: 18px;
    border-radius: 18px;
  }
  .score-main {
    padding-right: 15px;
  }
  .score-main strong {
    font-size: 60px;
  }
  .time-stats dd {
    font-size: 23px;
  }
  .result-actions .button {
    font-size: 12px;
    padding-inline: 10px;
  }
  .site-footer {
    padding-top: 26px;
  }
  html[lang=en] .pause-panel h1 {
    font-size: 24px;
  }
}
@media(max-width:360px) {
  main {
    padding: 0 14px;
  }
  .site-header {
    padding-inline: 15px;
  }
  .question-panel {
    padding-inline: 13px;
  }
  .key {
    min-height: 44px;
  }
  .question-hint {
    font-size: 10px;
  }
  .result-card {
    padding: 22px 15px;
  }
  .score-main strong {
    font-size: 52px;
  }
  .score-main p {
    font-size: 10px;
  }
  .time-stats dt {
    font-size: 10px;
  }
}
@media(prefers-reduced-motion:reduce) {
  *,*:before,*:after {
    animation: none!important;
    transition: none!important;
    scroll-behavior: auto!important;
  }
}