body {
  background: #e5e7eb;
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  margin: 0;
  font-family: Arial, sans-serif;
}

/* Calculator Body */
.calculator {
  background: #f8fafc;
  padding: 25px;
  border-radius: 18px;
  width: 330px;
  box-shadow:
    0 12px 25px rgba(0,0,0,0.25),
    0 4px 8px rgba(0,0,0,0.15),
    inset 0 1px 2px rgba(255,255,255,0.8);
}

/* Display Screen */
#display {
  width: 90%;
  height: 70px;
  font-size: 2.2rem;
  text-align: right;
  padding: 1px 15px; /* FIX: 15px, not 15x */
  border: none;
  border-radius: 10px;
  background: #e2e8f0;
  box-shadow:
    inset 0 4px 10px rgba(0,0,0,0.25),
    inset 0 -2px 4px rgba(255,255,255,0.4);
}

/* Button Grid */
.buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 14px;
  margin-top: 20px;
}

/* Base Button Style */
.btn,
.btn-operator,
.clear,
.equal {
  background: #ffffff;
  border: none;
  padding: 18px;
  font-size: 1.5rem;
  border-radius: 10px;
  cursor: pointer;
  box-shadow:
    0 6px 0 #cbd5e1,
    0 8px 15px rgba(0,0,0,0.15);
  transition: all 0.12s ease-in-out;
}

/* Pressed Button Effect */
.btn:active,
.btn-operator:active,
.clear:active,
.equal:active {
  transform: translateY(4px);
  box-shadow:
    0 2px 0 #cbd5e1,
    0 4px 8px rgba(0,0,0,0.2);
}

/* Operator Buttons */
.btn-operator {
  background: #f1f5f9;
}

/* Clear Button */
.clear {
  background: #fee2e2;
  color: #b91c1c;
  font-weight: bold;
}

/* Equal Button */
.equal {
  grid-column: span 4;
  background: #dbeafe;
  font-weight: bold;
  font-size: 1.6rem;
}