/* === Reset === */
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  font-family: "Poppins", sans-serif;
}

/* === Body === */
body {
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  background: radial-gradient(circle at center, #1e1e2f, #111);
}

/* === Calculator === */
.calculator {
  background: #222;
  padding: 20px;
  border-radius: 15px;
  box-shadow: 0 8px 20px rgba(0, 0, 0, 0.5);
  width: 300px;
}

/* === Display === */
#display {
  width: 100%;
  height: 60px;
  background: #000;
  border: none;
  color: #0f0;
  font-size: 2rem;
  text-align: right;
  padding-right: 10px;
  border-radius: 10px;
  margin-bottom: 15px;
}

/* === Buttons === */
.buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 10px;
}

.btn {
  height: 60px;
  border: none;
  border-radius: 10px;
  font-size: 1.2rem;
  background: #333;
  color: white;
  cursor: pointer;
  transition: all 0.2s;
}

.btn:hover {
  background: #444;
}

.operator {
  background: #ff9500;
}

.operator:hover {
  background: #e08900;
}

.equal {
  background: #00c853;
  grid-row: span 2;
}

.equal:hover {
  background: #00a43b;
}

.zero {
  grid-column: span 2;
}

#clear {
  background: #ff3b30;
}

#clear:hover {
  background: #d32f2f;
}

#backspace {
  background: #607d8b;
}

#backspace:hover {
  background: #546e7a;
}