:root {
  color-scheme: dark;
  --bg: #0f1115;
  --panel: #1a1d24;
  --key: #2a2f3a;
  --key-hover: #353b49;
  --op: #f5a524;
  --op-hover: #ffb640;
  --text: #f4f6fb;
  --muted: #9aa3b5;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-height: 100vh;
  font-family: "Inter", system-ui, sans-serif;
  background:
    radial-gradient(circle at top, #243049 0%, transparent 45%),
    var(--bg);
  color: var(--text);
}

.wrap {
  max-width: 360px;
  margin: 0 auto;
  padding: 2rem 1rem 3rem;
}

.back {
  display: inline-block;
  margin-bottom: 1.25rem;
  color: var(--muted);
  text-decoration: none;
  font-size: 0.9rem;
}

.back:hover {
  color: var(--text);
}

.calc {
  background: var(--panel);
  border-radius: 24px;
  padding: 1.25rem;
  box-shadow: 0 20px 50px rgba(0, 0, 0, 0.35);
}

.display {
  min-height: 4.5rem;
  margin-bottom: 1rem;
  padding: 0.75rem 0.5rem;
  text-align: right;
  font-size: clamp(2rem, 8vw, 2.75rem);
  font-weight: 600;
  letter-spacing: 0.02em;
  word-break: break-all;
}

.keys {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 0.65rem;
}

button {
  appearance: none;
  border: 0;
  border-radius: 999px;
  min-height: 3.4rem;
  font-size: 1.15rem;
  font-weight: 600;
  color: var(--text);
  background: var(--key);
  cursor: pointer;
}

button:hover {
  background: var(--key-hover);
}

button.op {
  background: var(--op);
  color: #1a1205;
}

button.op:hover {
  background: var(--op-hover);
}

button.muted {
  color: var(--muted);
}

.span-2 {
  grid-column: span 2;
}