:root {
  --bg: #1f2937;
  --fg: #f3f4f6;

  --cell-bg: #e5e7eb;
  --cell-fg: #111827;

  --row-bg: #dc2626;
  --col-bg: #2563eb;
  --half-bg: #16a34a;
  --sum-fg: #ffffff;

  --btn-bg: #9333ea;
  --btn-bg-hover: #7e22ce;
  --btn-bg-active: #6b21a8;
  --btn-ring: #c084fc;

  --radius: 0.375rem;
  --gap: 0.5rem;
}

* {
  box-sizing: border-box;
}

html, body {
  margin: 0;
  padding: 0;
  background: var(--bg);
  color: var(--fg);
  font-family: ui-sans-serif, system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
}

.dice-grid {
  max-width: 42rem;
  margin: 0 auto;
  padding: 2rem 1rem;
}

h1 {
  font-size: 1.875rem;
  font-weight: 700;
  margin: 0 0 1.5rem;
  text-align: center;
}

.controls {
  display: flex;
  gap: var(--gap);
  margin-bottom: 1.5rem;
  justify-content: center;
  flex-wrap: wrap;
}

.controls button {
  font: inherit;
  font-weight: 600;
  color: #fff;
  background: var(--btn-bg);
  border: none;
  padding: 0.5rem 1rem;
  border-radius: var(--radius);
  cursor: pointer;
  transition: background-color 120ms ease;
}

.controls button:hover {
  background: var(--btn-bg-hover);
}

.controls button.active {
  background: var(--btn-bg-active);
  outline: 2px solid var(--btn-ring);
  outline-offset: 1px;
}

.grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: var(--gap);
  max-width: 28rem;
  margin: 0 auto;
}

.cell {
  text-align: center;
  padding: 1rem 0;
  font-size: 1.5rem;
  font-weight: 700;
  border-radius: var(--radius);
  background: var(--cell-bg);
  color: var(--cell-fg);
}

.cell.row-sum {
  background: var(--row-bg);
  color: var(--sum-fg);
}

.cell.col-sum {
  background: var(--col-bg);
  color: var(--sum-fg);
}

.cell.half-sum {
  background: var(--half-bg);
  color: var(--sum-fg);
}

footer {
  display: flex;
  justify-content: center;
  gap: 1.25rem;
  margin-top: 1.5rem;
  font-size: 0.875rem;
}

footer a,
footer button {
  color: var(--fg);
  opacity: 0.7;
  background: none;
  border: none;
  padding: 0;
  font: inherit;
  cursor: pointer;
  text-decoration: underline;
}

footer a:hover,
footer button:hover {
  opacity: 1;
}

dialog {
  background: var(--bg);
  color: var(--fg);
  border: 1px solid var(--cell-bg);
  border-radius: var(--radius);
  padding: 1.5rem 1.75rem;
  max-width: 28rem;
}

dialog::backdrop {
  background: rgba(0, 0, 0, 0.5);
}

dialog h2 {
  margin: 0 0 0.75rem;
}

dialog p {
  margin: 0.5rem 0;
}

dialog ul {
  margin: 0.5rem 0;
  padding-left: 1.25rem;
}

dialog form {
  display: flex;
  justify-content: flex-end;
  margin-top: 1.25rem;
}

dialog form button {
  font: inherit;
  font-weight: 600;
  color: #fff;
  background: var(--btn-bg);
  border: none;
  padding: 0.5rem 1rem;
  border-radius: var(--radius);
  cursor: pointer;
  transition: background-color 120ms ease;
}

dialog form button:hover {
  background: var(--btn-bg-hover);
}