:root {
  color-scheme: light;
  --bg: #f6f7fb;
  --surface: #ffffff;
  --ink: #182033;
  --muted: #667085;
  --line: #d8deea;
  --number: #d8ecff;
  --number-ink: #17436b;
  --up: #dff5df;
  --up-ink: #17633a;
  --down: #ffe1df;
  --down-ink: #8a2d28;
  --equal: #eadfff;
  --equal-ink: #51307f;
  --blank: #fff7cf;
  --accent: #1b5fd6;
  --void: #eef2f8;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-height: 100vh;
  background: var(--bg);
  color: var(--ink);
  font-family:
    "Microsoft YaHei",
    "PingFang SC",
    "Noto Sans CJK SC",
    system-ui,
    sans-serif;
}

button,
input,
select {
  font: inherit;
}

.app-shell {
  display: grid;
  grid-template-columns: minmax(260px, 340px) minmax(0, 1fr);
  gap: 18px;
  width: min(1440px, 100%);
  margin: 0 auto;
  padding: 22px;
}

.toolbar,
.board-panel,
.equation-panel {
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: 8px;
}

.toolbar {
  display: flex;
  flex-direction: column;
  gap: 18px;
  align-self: start;
  padding: 20px;
}

h1,
h2,
p {
  margin: 0;
}

h1 {
  font-size: 28px;
  line-height: 1.15;
}

h2 {
  font-size: 18px;
}

p {
  color: var(--muted);
  line-height: 1.6;
}

.controls {
  display: grid;
  gap: 12px;
}

label {
  display: grid;
  gap: 6px;
  color: #344054;
  font-size: 14px;
}

select,
input[type="number"] {
  width: 100%;
  min-height: 38px;
  border: 1px solid var(--line);
  border-radius: 6px;
  padding: 8px 10px;
  background: #fff;
  color: var(--ink);
}

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

.operator-picker {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 8px;
  margin: 0;
  padding: 12px;
  border: 1px solid var(--line);
  border-radius: 8px;
}

.operator-picker legend {
  padding: 0 6px;
  color: var(--muted);
  font-size: 13px;
}

.operator-picker label {
  display: flex;
  align-items: center;
  justify-content: center;
  min-height: 36px;
  border: 1px solid var(--line);
  border-radius: 6px;
  background: #fbfcff;
  font-size: 16px;
}

.actions {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 10px;
}

button {
  min-height: 42px;
  border: 0;
  border-radius: 6px;
  background: var(--accent);
  color: #fff;
  cursor: pointer;
  font-weight: 700;
}

button.secondary {
  border: 1px solid var(--line);
  background: #fff;
  color: var(--ink);
}

.board-panel {
  min-width: 0;
  padding: 18px;
}

.board-header {
  display: flex;
  align-items: start;
  justify-content: space-between;
  gap: 16px;
  margin-bottom: 14px;
}

.legend {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  color: var(--muted);
  font-size: 13px;
}

.legend span {
  display: inline-flex;
  align-items: center;
  gap: 5px;
}

.legend i {
  width: 12px;
  height: 12px;
  border-radius: 3px;
}

.number-dot {
  background: var(--number);
}

.up-dot {
  background: var(--up);
}

.down-dot {
  background: var(--down);
}

.equal-dot {
  background: var(--equal);
}

.board {
  --size: 13;
  display: grid;
  grid-template-columns: repeat(var(--size), 48px);
  grid-template-rows: repeat(var(--size), 48px);
  gap: 3px;
  overflow-x: auto;
  align-items: stretch;
  justify-content: start;
  padding: 6px 0 4px;
}

.cell {
  display: grid;
  place-items: center;
  min-width: 0;
  min-height: 0;
  border: 1px solid var(--line);
  border-radius: 5px;
  background: #f7f9fc;
  color: transparent;
  font-size: clamp(13px, 1.45vw, 22px);
  font-weight: 800;
  line-height: 1;
}

.cell.empty {
  border-color: transparent;
  background: var(--void);
}

.cell.number {
  background: var(--number);
  color: var(--number-ink);
}

.cell.operator.up {
  background: var(--up);
  color: var(--up-ink);
}

.cell.operator.down {
  background: var(--down);
  color: var(--down-ink);
}

.cell.equal {
  background: var(--equal);
  color: var(--equal-ink);
}

.cell.blank {
  background: var(--blank);
  color: transparent;
  cursor: text;
  padding: 3px;
}

.cell.blank.reveal {
  outline: 2px solid #f0be24;
  color: #5a4100;
}

.cell.correct {
  outline: 2px solid #20a464;
  background: #e2f8ed;
}

.cell.incorrect {
  outline: 2px solid #d6453d;
  background: #ffe3e0;
}

.answer-input {
  width: 100%;
  height: 100%;
  min-width: 0;
  border: 2px solid #d9ad1e;
  border-radius: 5px;
  background: #fff;
  color: #533f00;
  text-align: center;
  font-size: clamp(13px, 1.35vw, 20px);
  font-weight: 800;
  line-height: 1;
  caret-color: var(--accent);
  appearance: none;
  box-shadow: inset 0 -2px 0 rgba(217, 173, 30, 0.35);
}

.answer-input:focus {
  border-color: var(--accent);
  outline: 2px solid rgba(27, 95, 214, 0.18);
}

.answer-input::placeholder {
  color: #b08a16;
}

.feedback {
  min-height: 24px;
  font-weight: 700;
}

@media (max-width: 900px) {
  .app-shell {
    grid-template-columns: 1fr;
    padding: 14px;
  }

  .board-header {
    display: grid;
  }
}