:root{
  --bg: #0f172a;
  --card:#0b1220;
  --accent:#0ea5ad;
  --muted:#94a3b8;
  --danger:#ef4444;
}
*{box-sizing:border-box;font-family:Inter, system-ui, Arial, sans-serif}
html,body{height:100%;margin:0;background:linear-gradient(180deg,#071022 0%,#0c1724 100%);display:flex;align-items:center;justify-content:center}
.calculator{width:360px;background:linear-gradient(180deg,var(--card),#06111a);border-radius:12px;padding:18px;box-shadow:0 8px 30px rgba(2,6,23,.6);color:#e6eef6}
.calc-header{text-align:center;font-weight:600;padding:6px 0;border-bottom:1px solid rgba(255,255,255,.03);margin-bottom:12px}
.display{width:100%;padding:12px 14px;border-radius:8px;background:rgba(255,255,255,0.04);border:1px solid rgba(255,255,255,0.03);color:#e6eef6;font-size:20px}
.calc-form{display:grid;gap:10px}
.row.keypad{display:flex;gap:8px}
.btn{flex:1;padding:12px;border-radius:8px;border:0;background:rgba(255,255,255,0.03);color:var(--muted);font-size:16px;cursor:pointer;transition: all 0.2s ease;}
.btn.small{padding:8px;font-size:13px}
.btn.op{background:rgba(14,165,173,0.08);color:var(--accent);}
.btn.equal{background:var(--accent);color:#022;flex:1}
.btn.light{background:rgba(255,255,255,0.02)}
.btn.danger{background:rgba(239,68,68,0.12);color:var(--danger)}
.btn.wide{flex:2}

/* Hover & Micro-interactions */
@media (hover: hover) {
  .btn:hover {
    transform: translateY(-2px);
    box-shadow: 0 4px 12px rgba(255, 255, 255, 0.05);
  }
  .btn.op:hover {
    box-shadow: 0 4px 12px rgba(14, 165, 173, 0.25);
  }
  .btn.equal:hover {
    box-shadow: 0 4px 15px rgba(14, 165, 173, 0.4);
  }
  .btn.danger:hover {
    box-shadow: 0 4px 12px rgba(239, 68, 68, 0.35);
  }
}

/* Active / Click feedback */
.btn:active {
  transform: translateY(0) scale(0.97) !important;
}

.row.extra .btn{font-size:14px}
.credits{font-size:12px;text-align:center;color:rgba(230,238,246,0.6);margin-top:10px}
@media (max-width:420px){.calculator{width:94%}}