:root{
  --page1:#fdfbfb;
  --page2:#ebedee;

  --card1:#ffffff;
  --card2:#f9fafb;

  --border:#e5e7eb;

  --text:#111827;
  --muted:#6b7280;

  --btn1:#ffffff;
  --btn2:#f3f4f6;

  --op1:#e0e7ff;
  --op2:#c7d2fe;

  --eq1:#34d399;
  --eq2:#059669;

  --ac1:#f87171;
  --ac2:#dc2626;

  --shadow: 0 20px 60px rgba(0,0,0,0.08);
}

*{
  box-sizing:border-box;
  font-family: system-ui, -apple-system, Segoe UI, Roboto, Arial, sans-serif;
}

body{
  margin:0;
  min-height:100vh;
  display:grid;
  place-items:center;
  background: linear-gradient(135deg, var(--page1), var(--page2));
  padding:24px;
  color:var(--text);
}

.calc{
  width:min(380px, 100%);
  background: linear-gradient(145deg, var(--card1), var(--card2));
  border:1px solid var(--border);
  border-radius:20px;
  box-shadow: var(--shadow);
  overflow:hidden;
}

.display{
  padding:20px 18px 14px;
  background: linear-gradient(145deg, #ffffff, #f3f4f6);
  border-bottom:1px solid var(--border);
}

.hint{
  font-size:12px;
  color:var(--muted);
  margin-bottom:10px;
}

#screen{
  width:100%;
  border:0;
  outline:none;
  background:transparent;
  color:var(--text);
  font-size:36px;
  text-align:right;
  padding:8px 0 2px;
  letter-spacing:.3px;
}

.keys{
  display:grid;
  grid-template-columns: repeat(4, 1fr);
  gap:12px;
  padding:16px;
}

button{
  border:1px solid var(--border);
  outline:none;
  padding:16px 12px;
  border-radius:14px;
  background: linear-gradient(145deg, var(--btn1), var(--btn2));
  color:var(--text);
  font-size:18px;
  cursor:pointer;
  user-select:none;
  box-shadow: 0 4px 10px rgba(0,0,0,.05);
  transition: all .15s ease;
}

button:hover{
  transform: translateY(-2px);
  box-shadow: 0 6px 14px rgba(0,0,0,.08);
}

button:active{
  transform: translateY(0px);
  box-shadow: 0 3px 8px rgba(0,0,0,.06);
}

button:focus-visible{
  outline: 3px solid rgba(59,130,246,.35);
  outline-offset: 2px;
}

/* Operator buttons */
.op{
  background: linear-gradient(145deg, var(--op1), var(--op2));
  border-color: var(--op2);
  color:#1e3a8a;
  font-weight:600;
}

/* Equal button */
.eq{
  background: linear-gradient(145deg, var(--eq1), var(--eq2));
  border:none;
  color:#fff;
  font-weight:800;
}

/* AC button */
.ac{
  background: linear-gradient(145deg, var(--ac1), var(--ac2));
  border:none;
  color:#fff;
  font-weight:700;
}

.wide{
  grid-column: span 2;
}