body{display:flex;align-items:center;justify-content:center;min-height:100vh;background:#eef2f7;font-family:system-ui}
.calculator{width:320px;background:#fff;padding:16px;border-radius:12px;box-shadow:0 6px 18px rgba(0,0,0,.08)}
.display{height:64px;background:#111;color:#fff;border-radius:8px;padding:12px;font-size:28px;text-align:right;overflow:hidden}
.keys{display:grid;grid-template-columns:repeat(4,1fr);gap:10px;margin-top:12px}
button{padding:16px;border-radius:8px;border:1px solid #e3e7ee;background:#fafafa;font-size:18px;cursor:pointer}
button[data-action="equals"]{grid-row:span 2;background:#111;color:#fff}