:root {
  --color-bg: #1a1a2e;
  --color-cell: #16213e;
  --color-cell-hover: #1a2744;
  --color-border: #0f3460;
  --color-zero: #5b8fb9;
  --color-one: #80b3e0;
  --color-sum: #e2b714;
  --color-sum-bg: #2a1f3d;
  --color-text: #eee;
  --size-cell: min(14vw, 72px);
  --size-sum: min(10vw, 56px);
  --duration-flip: 150ms;
}

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  min-height: 100dvh;
  background: var(--color-bg);
  color: var(--color-text);
  font-family: system-ui, sans-serif;
}

h1 {
  margin-bottom: 8px;
  font-size: 1.5rem;
  letter-spacing: 0.05em;
  text-transform: uppercase;
}

.level-label {
  margin-bottom: 16px;
  font-size: 0.9rem;
  opacity: 0.6;
  letter-spacing: 0.08em;
}

.win-message {
  margin-top: 24px;
  padding: 12px 32px;
  font-size: 1.1rem;
  font-weight: 700;
  color: #52b788;
  background: #1b4332;
  border-radius: 8px;
  letter-spacing: 0.05em;
}

.grid {
  display: grid;
  column-gap: var(--size-sum);
  row-gap: var(--size-sum);
  position: relative;
}

.cell {
  display: flex;
  align-items: center;
  justify-content: center;
  background: var(--color-cell);
  border: 2px solid var(--color-border);
  border-radius: 8px;
  font-size: calc(var(--size-cell) * 0.5);
  font-weight: 700;
  cursor: pointer;
  user-select: none;
  transition:
    background var(--duration-flip),
    transform var(--duration-flip);

  &:hover {
    background: var(--color-cell-hover);
  }

  &:active {
    transform: scale(0.92);
  }

  &.zero {
    color: var(--color-zero);
  }

  &.one {
    color: var(--color-one);
  }
}

.sum-cell {
  position: absolute;
  width: var(--size-sum);
  height: var(--size-sum);
  display: flex;
  align-items: center;
  justify-content: center;
  background: var(--color-sum-bg);
  border-radius: 50%;
  font-size: calc(var(--size-sum) * 0.5);
  font-weight: 700;
  color: var(--color-sum);
  pointer-events: none;
  transition:
    background var(--duration-flip),
    color var(--duration-flip);

  &.correct {
    background: #1b4332;
    color: #52b788;
  }

  &.wrong {
    background: #3d1f1f;
    color: #e94560;
  }
}