body {
  background: #f4f4f4;
  font-family: Arial, sans-serif;
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
}

.calculator {
  background: #fff;
  padding: 30px 20px;
  border-radius: 10px;
  box-shadow: 0 4px 12px rgba(0,0,0,0.12);
  width: 260px;
}

.display {
  width: 100%;
  height: 40px;
  font-size: 1.5em;
  margin-bottom: 18px;
  text-align: right;
  padding: 8px;
  border: 1px solid #ddd;
  border-radius: 5px;
}

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

button {
  padding: 16px 0;
  font-size: 1.2em;
  border: none;
  border-radius: 6px;
  background: #eee;
  cursor: pointer;
  transition: background 0.2s;
}

button:active {
  background: #ccc;
}

.equal {
  grid-column: span 4;
  background: #2980b9;
  color: #fff;
  font-weight: bold;
}