:root {
  color-scheme: light;
  --ink: #1f2937;
  --muted: #687083;
  --line: #d8dee8;
  --paper: #fffdf7;
  --panel: #ffffff;
  --chalk: #263247;
  --green: #2f8d68;
  --blue: #3e75d8;
  --yellow: #f5c84c;
  --red: #ef6b57;
  --violet: #7465c9;
  --cyan: #80cde4;
  --shadow: 0 18px 48px rgba(31, 41, 55, 0.13);
}

* {
  box-sizing: border-box;
}

body {
  min-height: 100vh;
  margin: 0;
  background:
    linear-gradient(180deg, rgba(223, 238, 252, 0.95), rgba(255, 253, 247, 0.98) 45%),
    var(--paper);
  color: var(--ink);
  font-family:
    "PingFang SC", "Microsoft YaHei", "Noto Sans CJK SC", system-ui, sans-serif;
}

body[data-version="a"] {
  background:
    linear-gradient(180deg, #eaf0f7, #f8fafc 46%),
    #f8fafc;
}

body[data-version="b"] {
  background:
    radial-gradient(circle at 12% 10%, rgba(245, 200, 76, 0.36), transparent 18%),
    linear-gradient(180deg, #dff1ff 0, #fff5d7 44%, #f3fff1 100%);
}

button,
select {
  font: inherit;
}

button,
select {
  border-radius: 8px;
}

button {
  border: 1px solid var(--line);
  background: #fff;
  color: var(--ink);
  cursor: pointer;
  font-weight: 800;
}

.shell {
  width: min(1280px, calc(100vw - 40px));
  margin: 0 auto;
  padding: 28px 0 42px;
}

.hero {
  display: flex;
  align-items: end;
  justify-content: space-between;
  gap: 22px;
  margin-bottom: 16px;
}

.kicker,
.lesson-info > p {
  margin: 0 0 8px;
  color: var(--green);
  font-size: 14px;
  font-weight: 800;
}

h1,
h2,
h3,
p {
  letter-spacing: 0;
}

h1 {
  margin: 0;
  font-size: clamp(34px, 5vw, 58px);
  line-height: 1.05;
}

h2 {
  margin: 0;
  font-size: 26px;
  line-height: 1.18;
}

.hero-note {
  display: grid;
  min-width: 150px;
  padding: 14px 16px;
  border: 1px solid #efd684;
  border-radius: 8px;
  background: #fff7d9;
  box-shadow: var(--shadow);
}

.hero-note span {
  color: #9a6616;
  font-size: 22px;
  font-weight: 950;
}

.hero-note strong {
  color: #6c4b13;
  font-size: 14px;
}

.control-strip {
  display: grid;
  grid-template-columns: minmax(300px, 1fr) auto auto;
  gap: 12px;
  align-items: end;
  margin-bottom: 14px;
}

.control-strip label,
.version-switch {
  display: grid;
  gap: 8px;
  margin: 0;
  padding: 0;
  border: 0;
}

.control-strip label span,
.version-switch legend {
  color: var(--muted);
  font-size: 14px;
  font-weight: 800;
}

select {
  width: 100%;
  min-height: 48px;
  padding: 0 14px;
  border: 1px solid var(--line);
  background: #fff;
  color: var(--ink);
  font-weight: 750;
}

.version-switch {
  grid-template-columns: repeat(2, 122px);
}

.version-switch legend {
  grid-column: 1 / -1;
}

.version,
.reset-button {
  min-height: 48px;
  padding: 0 16px;
}

.version.active,
.reset-button {
  background: var(--chalk);
  color: #fff;
  border-color: var(--chalk);
}

body[data-version="b"] .version.active {
  background: #f4b740;
  color: #3c2a05;
  border-color: #c88918;
  box-shadow: inset 0 -3px 0 rgba(120, 78, 8, 0.18);
}

body[data-version="b"] .hero-note {
  border-color: #f2bd63;
  background: #fff0bc;
}

.lesson-frame {
  display: grid;
  grid-template-columns: 310px minmax(0, 1fr);
  min-height: 650px;
  border: 1px solid var(--line);
  border-radius: 8px;
  overflow: hidden;
  background: rgba(255, 255, 255, 0.9);
  box-shadow: var(--shadow);
}

.lesson-info {
  padding: 28px;
  border-right: 1px solid var(--line);
  background: #fbf8ee;
}

.objective,
.teacher-tip {
  margin-top: 18px;
  padding: 16px;
  border-radius: 8px;
  line-height: 1.58;
}

.objective {
  background: #eef7ff;
  color: #225185;
  border: 1px solid #c4daf4;
  font-weight: 800;
}

.teacher-tip {
  background: #eaf7ee;
  color: #276348;
  border: 1px solid #bde0c8;
}

.tool-stage {
  position: relative;
  min-width: 0;
  padding: 28px;
  background: #fff;
}

.tool-stage.version-a {
  background:
    linear-gradient(90deg, rgba(38, 50, 71, 0.04) 1px, transparent 1px),
    linear-gradient(180deg, rgba(38, 50, 71, 0.04) 1px, transparent 1px),
    #f8fafc;
  background-size: 28px 28px;
}

.tool-stage.version-b {
  background:
    radial-gradient(circle at 92% 8%, rgba(245, 200, 76, 0.28), transparent 18%),
    linear-gradient(180deg, #fff7e4, #edf7ff 60%, #f6fff5);
}

.tool-card {
  min-height: 590px;
  display: grid;
  gap: 18px;
  align-content: start;
}

.version-a .tool-card {
  padding: 2px;
}

.version-b .tool-card {
  gap: 20px;
}

.tool-head {
  display: flex;
  justify-content: space-between;
  gap: 16px;
  align-items: center;
}

.tool-head h3 {
  margin: 0;
  font-size: 30px;
  line-height: 1.15;
}

.tool-badge {
  display: inline-grid;
  place-items: center;
  min-width: 88px;
  min-height: 42px;
  padding: 0 12px;
  border-radius: 8px;
  background: #fff7d9;
  color: #80530d;
  font-weight: 950;
}

.version-a .tool-badge {
  background: var(--chalk);
  color: #fff;
}

.version-b .tool-badge {
  background: #fff2bd;
  color: #86580c;
  border: 1px solid #f0c468;
  transform: rotate(-1deg);
}

.version-note {
  display: grid;
  grid-template-columns: auto 1fr;
  gap: 10px;
  align-items: center;
  min-height: 48px;
  padding: 12px 14px;
  border-radius: 8px;
  font-size: 16px;
}

.version-note strong {
  white-space: nowrap;
}

.version-a .version-note {
  border: 1px solid #c8d1df;
  background: #ffffff;
  color: #344054;
}

.version-a .version-note strong {
  color: var(--chalk);
}

.version-b .version-note {
  border: 1px solid #f0ca76;
  background: #fff7d9;
  color: #75520e;
}

.version-b .version-note strong {
  color: #b25a28;
}

.board {
  position: relative;
  min-height: 390px;
  border: 1px solid var(--line);
  border-radius: 8px;
  overflow: hidden;
  background:
    linear-gradient(180deg, #dcefff 0 56%, #dff2c9 56%),
    #f6fbff;
}

.version-a .board {
  border: 6px solid #344054;
  background:
    linear-gradient(rgba(255, 255, 255, 0.06) 1px, transparent 1px),
    linear-gradient(90deg, rgba(255, 255, 255, 0.06) 1px, transparent 1px),
    #1f2a38;
  background-size: 36px 36px;
  box-shadow: inset 0 0 0 1px rgba(255, 255, 255, 0.08);
}

.version-b .board {
  border-color: #f1d190;
  background:
    radial-gradient(circle at 12% 18%, #ffd967 0 38px, transparent 40px),
    linear-gradient(180deg, #ffe8b8 0 46%, #bfead4 46%),
    #fff7e4;
  box-shadow: inset 0 -24px 0 rgba(73, 156, 102, 0.12);
}

.action-row,
.number-row,
.symbol-row {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
}

.action-row button,
.number-row button,
.symbol-row button,
.choice-chip {
  min-height: 50px;
  padding: 0 18px;
  border-radius: 8px;
  border: 1px solid var(--line);
  background: #fff;
  color: var(--ink);
  font-weight: 900;
}

.version-a .action-row button,
.version-a .number-row button,
.version-a .symbol-row button,
.version-a .choice-chip {
  background: #ffffff;
  border-color: #c8d1df;
  color: #243042;
  box-shadow: 0 2px 0 #c8d1df;
}

.version-b .action-row button,
.version-b .number-row button,
.version-b .symbol-row button,
.version-b .choice-chip {
  min-height: 56px;
  background: #fff7d9;
  border-color: #eabc58;
  color: #6f4b0f;
  box-shadow: 0 4px 0 rgba(172, 112, 22, 0.18);
}

.number-row button {
  min-width: 64px;
  font-size: 26px;
}

.symbol-row button {
  min-width: 70px;
  font-size: 28px;
}

.action-row button.primary,
.choice-chip.active,
.symbol-row button.active {
  background: var(--blue);
  color: #fff;
  border-color: var(--blue);
}

.version-b .action-row button.primary,
.version-b .choice-chip.active,
.version-b .symbol-row button.active {
  background: #ef7a56;
  border-color: #d65d39;
  color: #fff;
}

.feedback {
  min-height: 64px;
  display: grid;
  align-items: center;
  padding: 14px 16px;
  border-radius: 8px;
  background: #eef7ff;
  border: 1px solid #c4daf4;
  color: #244e82;
  font-size: 18px;
  font-weight: 850;
}

.version-a .feedback {
  border-left: 8px solid var(--blue);
  background: #f8fbff;
}

.version-b .feedback {
  min-height: 72px;
  border: 2px solid #f0ca76;
  background: #fff8df;
  color: #77510d;
  font-size: 19px;
  box-shadow: 0 8px 0 rgba(239, 177, 72, 0.12);
}

.feedback.good {
  background: #eaf7ee;
  border-color: #bde0c8;
  color: #276348;
}

.feedback.try {
  background: #fff0ec;
  border-color: #f1b5a8;
  color: #963d2d;
}

.review-panel {
  border: 1px solid var(--line);
  border-radius: 8px;
  overflow: hidden;
  background: #fff;
}

.version-a .review-panel {
  border-color: #c8d1df;
}

.version-b .review-panel {
  border: 2px solid #f0ca76;
  background: #fff8df;
  box-shadow: 0 8px 0 rgba(239, 177, 72, 0.1);
}

.review-toggle {
  display: flex;
  align-items: center;
  justify-content: space-between;
  width: 100%;
  min-height: 58px;
  padding: 0 18px;
  border: 0;
  border-radius: 0;
  background: #f8fbff;
  color: var(--ink);
  text-align: left;
}

.version-a .review-toggle {
  background: #eef2f7;
}

.version-b .review-toggle {
  background: #fff0bc;
  color: #73500e;
}

.review-toggle span {
  font-size: 20px;
  font-weight: 950;
}

.review-toggle strong {
  font-size: 15px;
}

.review-body {
  display: grid;
  gap: 14px;
  padding: 18px;
}

.review-login {
  display: grid;
  grid-template-columns: 150px 150px auto;
  gap: 10px;
  align-items: center;
}

.review-login.logged-in {
  grid-template-columns: 1fr auto;
  min-height: 48px;
  padding: 0 12px;
  border-radius: 8px;
  background: #eaf7ee;
  color: #276348;
  font-weight: 850;
}

.review-login input,
.review-form textarea {
  width: 100%;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: #fff;
  color: var(--ink);
  font: inherit;
}

.review-login input {
  min-height: 46px;
  padding: 0 12px;
}

.review-login button,
.review-form button,
.review-item button {
  min-height: 46px;
  padding: 0 16px;
}

.review-form {
  display: grid;
  grid-template-columns: 1fr auto;
  gap: 10px;
  align-items: end;
}

.review-form textarea {
  min-height: 90px;
  resize: vertical;
  padding: 12px;
  line-height: 1.5;
}

.review-form button {
  background: var(--chalk);
  color: #fff;
  border-color: var(--chalk);
}

.version-b .review-form button {
  background: #ef7a56;
  border-color: #d65d39;
}

.review-error,
.review-empty {
  padding: 12px 14px;
  border-radius: 8px;
  font-weight: 800;
}

.review-error {
  background: #fff0ec;
  color: #963d2d;
  border: 1px solid #f1b5a8;
}

.review-empty {
  background: #f8fafc;
  color: var(--muted);
  border: 1px dashed #c8d1df;
}

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

.review-item {
  display: grid;
  gap: 10px;
  padding: 14px;
  border: 1px solid #d8dee8;
  border-radius: 8px;
  background: #ffffff;
}

.version-b .review-item {
  border-color: #f0ca76;
  background: #fffdf3;
}

.review-item header {
  display: flex;
  justify-content: space-between;
  gap: 12px;
  color: var(--muted);
  font-size: 14px;
}

.review-item header strong {
  color: var(--ink);
}

.review-item p {
  margin: 0;
  white-space: pre-wrap;
  line-height: 1.6;
}

.review-item button {
  justify-self: start;
  color: #963d2d;
  border-color: #f1b5a8;
  background: #fff0ec;
}

.big-number {
  display: inline-grid;
  place-items: center;
  width: 86px;
  height: 86px;
  border-radius: 50%;
  background: var(--chalk);
  color: #fff;
  font-size: 44px;
  font-weight: 950;
}

.objects-grid {
  display: grid;
  grid-template-columns: repeat(5, minmax(52px, 1fr));
  gap: 16px;
  align-content: center;
  justify-items: center;
  min-height: 100%;
  padding: 34px;
}

.obj {
  display: grid;
  place-items: center;
  width: 66px;
  height: 66px;
  border-radius: 50%;
  background: var(--red);
  color: #fff;
  font-size: 34px;
  font-weight: 950;
  box-shadow: inset -10px -10px 0 rgba(0, 0, 0, 0.12);
  animation: pop 220ms ease both;
}

.version-a .obj {
  border-radius: 8px;
  background: #e8f0ff;
  color: #1f2a38;
  border: 2px solid #91a7d8;
  box-shadow: inset 0 -8px 0 rgba(62, 117, 216, 0.18);
}

.version-b .obj {
  width: 72px;
  height: 72px;
  border: 4px solid rgba(255, 255, 255, 0.74);
  background: radial-gradient(circle at 35% 28%, #ffd7c8 0 12px, var(--red) 13px);
  box-shadow:
    inset -10px -10px 0 rgba(112, 40, 28, 0.15),
    0 8px 0 rgba(170, 83, 54, 0.14);
}

.obj.square {
  border-radius: 8px;
  background: var(--blue);
}

.version-b .obj.square {
  border-radius: 22px;
  background: radial-gradient(circle at 35% 28%, #d9efff 0 12px, #5c9ded 13px);
}

.obj.rod {
  width: 34px;
  height: 96px;
  border-radius: 18px;
  background: var(--yellow);
  color: #74500e;
}

.obj.empty {
  background: #fff;
  border: 2px dashed #c4cbd8;
  box-shadow: none;
}

.split-board {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 18px;
}

.bin {
  min-height: 260px;
  padding: 18px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: #fff8e7;
}

.version-a .bin {
  background: #ffffff;
  border-color: #c8d1df;
}

.version-b .bin {
  border: 2px solid #f0ca76;
  background: rgba(255, 248, 223, 0.92);
  box-shadow: 0 8px 0 rgba(239, 177, 72, 0.1);
}

.bin h4 {
  margin: 0 0 14px;
  color: #80530d;
}

.bin .objects-grid {
  min-height: 180px;
  padding: 0;
  grid-template-columns: repeat(4, 1fr);
}

.formula-line {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 12px;
  font-size: 38px;
  font-weight: 950;
}

.formula-box {
  display: inline-grid;
  place-items: center;
  min-width: 72px;
  min-height: 60px;
  padding: 0 14px;
  border-radius: 8px;
  background: #fff7d9;
  color: #80530d;
  border: 1px solid #efd684;
}

.version-a .formula-box {
  background: #ffffff;
  color: #1f2a38;
  border: 2px solid #344054;
}

.version-b .formula-box {
  border: 2px solid #f0b25a;
  background: #fff0bc;
  color: #8b5510;
  box-shadow: 0 4px 0 rgba(176, 108, 22, 0.14);
}

.ten-frame {
  display: grid;
  grid-template-columns: repeat(5, 72px);
  gap: 10px;
  justify-content: center;
  align-content: center;
  min-height: 310px;
}

.ten-cell {
  display: grid;
  place-items: center;
  width: 72px;
  height: 72px;
  border: 2px solid #b9c3d4;
  border-radius: 8px;
  background: #fff;
}

.version-a .ten-cell {
  background: rgba(255, 255, 255, 0.94);
  border-color: #94a3b8;
}

.version-b .ten-cell {
  border-color: #e6b45c;
  background: #fffdf3;
  box-shadow: 0 4px 0 rgba(176, 108, 22, 0.12);
}

.ten-cell.filled::before {
  content: "";
  width: 46px;
  height: 46px;
  border-radius: 50%;
  background: var(--red);
}

.place-board {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 18px;
}

.place-column {
  min-height: 320px;
  padding: 18px;
  border-radius: 8px;
  border: 1px solid var(--line);
  background: #f8fbff;
}

.version-a .place-column {
  background: #ffffff;
  border-color: #c8d1df;
}

.version-b .place-column {
  background: #fff8df;
  border: 2px solid #f0ca76;
}

.place-column h4 {
  margin: 0 0 14px;
  color: var(--blue);
  font-size: 22px;
}

.bundle {
  width: 72px;
  height: 150px;
  border-radius: 8px;
  background:
    repeating-linear-gradient(90deg, #f2b94d 0 5px, #9a6a22 5px 7px);
  border: 3px solid #9a6a22;
}

.number-line {
  position: relative;
  min-height: 180px;
  margin: 36px 8px 10px;
}

.number-line::before {
  content: "";
  position: absolute;
  left: 4%;
  right: 4%;
  top: 72px;
  height: 4px;
  border-radius: 4px;
  background: var(--chalk);
}

.tick {
  position: absolute;
  top: 48px;
  transform: translateX(-50%);
  text-align: center;
  font-weight: 900;
}

.tick::before {
  content: "";
  display: block;
  width: 4px;
  height: 48px;
  margin: 0 auto 8px;
  border-radius: 4px;
  background: var(--chalk);
}

.tick.active {
  color: var(--red);
}

.tick.active::before {
  background: var(--red);
}

.solid-grid {
  display: grid;
  grid-template-columns: repeat(4, minmax(120px, 1fr));
  gap: 16px;
}

.solid-card {
  display: grid;
  gap: 10px;
  place-items: center;
  min-height: 170px;
  padding: 16px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: #fff;
}

.version-a .solid-card {
  border-color: #c8d1df;
  background: #f8fafc;
}

.version-b .solid-card {
  border: 2px solid #f0ca76;
  background: #fff8df;
  box-shadow: 0 8px 0 rgba(239, 177, 72, 0.1);
}

.solid-shape {
  width: 86px;
  height: 86px;
  display: grid;
  place-items: center;
  color: #fff;
  font-weight: 950;
}

.cube {
  border-radius: 8px;
  background: linear-gradient(135deg, #5a89e6, #244a9b);
}

.box {
  width: 112px;
  border-radius: 8px;
  background: linear-gradient(135deg, #39a874, #1f7650);
}

.cylinder {
  border-radius: 50% / 16%;
  background: linear-gradient(90deg, #eaa44f, #c56d2e, #eaa44f);
}

.ball {
  border-radius: 50%;
  background: radial-gradient(circle at 30% 25%, #fff, #e35e69 28%, #9c2632 80%);
}

.blocks {
  display: grid;
  grid-template-columns: repeat(6, 56px);
  grid-auto-rows: 56px;
  gap: 8px;
  justify-content: center;
  align-content: end;
  min-height: 320px;
}

.block {
  border-radius: 8px;
  background: var(--blue);
  box-shadow: inset -8px -8px 0 rgba(0, 0, 0, 0.12);
}

.version-a .block {
  background: #5b6f95;
}

.version-b .block {
  background: #5c9ded;
  border: 3px solid rgba(255, 255, 255, 0.72);
}

.people-line {
  display: flex;
  align-items: end;
  justify-content: center;
  gap: 10px;
  min-height: 280px;
}

.person {
  display: grid;
  place-items: center;
  width: 52px;
  height: 88px;
  border-radius: 28px 28px 8px 8px;
  background: var(--cyan);
  color: #0e5365;
  font-weight: 950;
}

.version-a .person {
  border-radius: 8px;
  background: #e8f0ff;
  color: #1f2a38;
  border: 2px solid #91a7d8;
}

.version-b .person {
  border-radius: 28px 28px 12px 12px;
  background: #91ddcf;
}

.person.mark {
  background: var(--red);
  color: #fff;
}

.problem-panel {
  display: grid;
  gap: 14px;
  padding: 22px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: #f8fbff;
}

.version-a .problem-panel {
  background: #ffffff;
  border-color: #c8d1df;
}

.version-b .problem-panel {
  background: #fff8df;
  border: 2px solid #f0ca76;
}

.problem-panel p {
  margin: 0;
  font-size: 23px;
  line-height: 1.55;
  font-weight: 850;
}

input[type="range"] {
  width: min(520px, 100%);
  accent-color: var(--blue);
}

@keyframes pop {
  from {
    opacity: 0;
    transform: scale(0.72) translateY(16px);
  }
}

@media (max-width: 920px) {
  .hero,
  .control-strip,
  .lesson-frame,
  .place-board,
  .split-board {
    grid-template-columns: 1fr;
  }

  .hero {
    align-items: start;
  }

  .lesson-info {
    border-right: 0;
    border-bottom: 1px solid var(--line);
  }

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

  .review-login,
  .review-form {
    grid-template-columns: 1fr;
  }
}