:root {
  color-scheme: light;
  --bg: #edf1f4;
  --calculator: #f9fafb;
  --display: #172026;
  --display-text: #f8fbfc;
  --key: #ffffff;
  --key-hover: #eef3f7;
  --function: #dfe7ee;
  --operator: #ff9f1c;
  --operator-hover: #ee8f0d;
  --equals: #2563eb;
  --equals-hover: #1d4ed8;
  --text: #18202a;
  --muted: #65707d;
  --line: #cad3dc;
  --shadow: 0 22px 56px rgb(24 32 42 / 16%);
  --radius: 8px;
  font-family:
    Inter, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI",
    sans-serif;
}

@media (prefers-color-scheme: dark) {
  :root {
    color-scheme: dark;
    --bg: #101419;
    --calculator: #1a2028;
    --display: #05080c;
    --display-text: #f8fbfc;
    --key: #2a333e;
    --key-hover: #354150;
    --function: #3b4654;
    --operator: #f59e0b;
    --operator-hover: #d97706;
    --equals: #3b82f6;
    --equals-hover: #2563eb;
    --text: #f3f6f8;
    --muted: #a7b1bd;
    --line: #364250;
    --shadow: 0 22px 56px rgb(0 0 0 / 32%);
  }
}

* {
  box-sizing: border-box;
}

body {
  min-width: 320px;
  min-height: 100vh;
  margin: 0;
  color: var(--text);
  background: var(--bg);
}

body,
button {
  font: inherit;
}

button {
  color: inherit;
}

.skip-link {
  position: fixed;
  top: 1rem;
  left: 1rem;
  z-index: 10;
  padding: 0.65rem 0.85rem;
  border-radius: var(--radius);
  background: var(--display);
  color: var(--display-text);
  transform: translateY(-150%);
}

.skip-link:focus {
  transform: translateY(0);
}

.app-shell {
  display: grid;
  min-height: 100vh;
  place-items: center;
  padding: 1rem;
}

.calculator {
  width: min(100%, 380px);
  padding: 1rem;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--calculator);
  box-shadow: var(--shadow);
}

.calculator-header {
  margin-bottom: 0.85rem;
}

.eyebrow {
  margin: 0 0 0.25rem;
  color: var(--muted);
  font-size: 0.75rem;
  font-weight: 800;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

h1 {
  margin: 0;
  font-size: 1.5rem;
  line-height: 1.1;
  letter-spacing: 0;
}

.display {
  display: block;
  width: 100%;
  min-height: 5.5rem;
  margin-bottom: 0.85rem;
  padding: 1rem;
  overflow: hidden;
  border-radius: var(--radius);
  background: var(--display);
  color: var(--display-text);
  font-size: 2.5rem;
  font-weight: 800;
  line-height: 1.25;
  text-align: right;
  text-overflow: ellipsis;
  white-space: nowrap;
}

.keypad {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: 0.6rem;
}

.key {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-height: 4rem;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--key);
  font-size: 1.25rem;
  font-weight: 800;
  cursor: pointer;
}

.key:hover,
.key:focus-visible {
  background: var(--key-hover);
}

.key:focus-visible {
  outline: 3px solid rgb(37 99 235 / 35%);
  outline-offset: 2px;
}

.function {
  background: var(--function);
}

.operator {
  background: var(--operator);
  color: #111827;
}

.operator:hover,
.operator:focus-visible {
  background: var(--operator-hover);
}

.equals {
  background: var(--equals);
  color: white;
}

.equals:hover,
.equals:focus-visible {
  background: var(--equals-hover);
}

.zero {
  grid-column: span 2;
}

@media (max-width: 420px) {
  .calculator {
    padding: 0.75rem;
  }

  .display {
    min-height: 4.75rem;
    font-size: 2rem;
  }

  .key {
    min-height: 3.35rem;
  }
}