:root {
  --bg: #0f1220;
  --panel: #171a2b;
  --key: #22263a;
  --key-ac: #ff5a6e;
  --key-op: #3d7bff;
  --key-eq: #22c55e;
  --text: #e5e7eb;
  --muted: #9aa0b4;
  --shadow: 0 10px 25px rgba(0,0,0,.35);
  --radius: 22px;
}
* { box-sizing: border-box; }
html, body { height: 100%; }
body {
  margin: 0;
  display: grid;
  place-items: center;
  background: radial-gradient(1200px 600px at 10% 10%, #131733 0%, #0b0e1a 50%, #070912 100%), var(--bg);
  color: var(--text);
  font: 500 16px/1.4 system-ui, -apple-system, Segoe UI, Roboto, Ubuntu, Cantarell, Noto Sans, Helvetica, Arial, "Apple Color Emoji","Segoe UI Emoji";
}

.calc {
  width: min(92vw, 420px);
  background: linear-gradient(180deg, rgba(255,255,255,.04), rgba(255,255,255,0)), var(--panel);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 18px;
  display: flex;
  flex-direction: column;
  gap: 14px;
}

.display {
  background: rgba(255,255,255,.03);
  border-radius: 18px;
  padding: 18px 16px;
  min-height: 96px;
  display: flex;
  flex-direction: column;
  justify-content: center;
  gap: 6px;
  overflow: hidden;
  word-break: break-all;
  user-select: none;
}
.history { color: var(--muted); font-size: 0.95rem; min-height: 1.2em; letter-spacing: .5px; }
.current { font-size: 2.2rem; font-weight: 700; text-align: right; }

.keys { display: grid; grid-template-columns: repeat(4, 1fr); gap: 10px; }
button {
  appearance: none;
  border: 0;
  outline: 0;
  cursor: pointer;
  border-radius: 14px;
  padding: 16px;
  font-size: 1.05rem;
  font-weight: 700;
  color: var(--text);
  background: var(--key);
  box-shadow: inset 0 -2px 0 rgba(255,255,255,.03), var(--shadow);
  transition: transform .05s ease, filter .15s ease, background .2s ease;
}
button:active { transform: translateY(2px) scale(.99); filter: brightness(1.05); }
.op { background: #20305c; }
.eq { background: linear-gradient(180deg, rgba(255,255,255,.08), rgba(255,255,255,0)), var(--key-eq); color: #07140b; }
.ac { background: linear-gradient(180deg, rgba(255,255,255,.08), rgba(255,255,255,0)), var(--key-ac); color: #23070b; }
.wide { grid-column: span 2; }

@media (max-width: 420px) {
  .current { font-size: 8.5vw; }
  button { padding: 14px; font-size: 1rem; }
}