/* Calculator styles */
:root{--bg:#f3f7fb;--panel:#ffffff;--accent:#2b6cb0;--muted:#6b7280}
*{box-sizing:border-box}
html,body{height:100%;margin:0;font-family:Segoe UI, Roboto, Arial, sans-serif;background:var(--bg);color:#0f1720}
.calculator{max-width:360px;margin:3rem auto;padding:1rem;border-radius:12px;background:var(--panel);box-shadow:0 6px 20px rgba(12,17,35,.08)}
.display{background:#0f1720;color:#fff;padding:1.25rem;border-radius:8px;font-size:1.75rem;text-align:right;margin-bottom:1rem;min-height:56px}
.keys{display:grid;grid-template-columns:repeat(4,1fr);gap:.5rem}
.key{padding:.9rem;font-size:1.1rem;border-radius:8px;border:0;background:#f1f5f9;cursor:pointer}
.key.operator{background:var(--accent);color:#fff}
.key.equal{grid-column:4 / 5;background:#0ea5a4;color:#fff}
.key.zero{grid-column:1 / 3}
.back-link{margin-top:1rem;text-align:center}
.back-link a{color:var(--accent);text-decoration:none}
@media (max-width:420px){.calculator{margin:1rem}}