:root {
  color-scheme: light dark;
  --bg: #f3f4f6;
  --panel: #ffffff;
  --key: #f9fafb;
  --key-edge: #e5e7eb;
  --ink: #111827;
  --fn: #6b7280;
  --op: #0284c7;
  --op-ink: #ffffff;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #0b1020;
    --panel: #111827;
    --key: #1f2937;
    --key-edge: #374151;
    --ink: #f9fafb;
    --fn: #9ca3af;
    --op: #0ea5e9;
    --op-ink: #04121e;
  }
}

* { box-sizing: border-box; }

body {
  margin: 0;
  min-height: 100dvh;
  display: grid;
  place-items: center;
  padding: 16px;
  background: var(--bg);
  color: var(--ink);
  font: 16px/1.4 system-ui, sans-serif;
}

main {
  width: min(100%, 22rem);
  background: var(--panel);
  border: 1px solid var(--key-edge);
  border-radius: 14px;
  padding: 14px;
  box-shadow: 0 10px 30px rgb(0 0 0 / 0.08);
}

output {
  display: block;
  /* Long results shrink rather than overflow the panel. */
  font-size: clamp(1.75rem, 12vw, 2.75rem);
  font-variant-numeric: tabular-nums;
  text-align: right;
  padding: 8px 10px 16px;
  min-height: 1.4em;
  overflow-wrap: anywhere;
}

.pad {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 8px;
}

button {
  font: inherit;
  font-size: 1.15rem;
  padding: 0;
  height: 3.2rem;
  color: var(--ink);
  background: var(--key);
  border: 1px solid var(--key-edge);
  border-radius: 10px;
  cursor: pointer;
  /* Taps shouldn't select the glyph or fire the 300ms zoom delay. */
  user-select: none;
  touch-action: manipulation;
}

button:hover { border-color: var(--fn); }
button:active { transform: translateY(1px); }
button:focus-visible { outline: 2px solid var(--op); outline-offset: 2px; }

.fn { color: var(--fn); }

.op {
  background: var(--op);
  border-color: var(--op);
  color: var(--op-ink);
  font-weight: 600;
}

.wide { grid-column: span 2; }

@media (prefers-reduced-motion: reduce) {
  button:active { transform: none; }
}