* {
  box-sizing: border-box;
}

body {
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  background: #f9f6ee;
  font-family: 'Roboto', sans-serif;
}

.calculator {
  border-radius: 10px;
  overflow: hidden;
  box-shadow: 0 0 20px rgba(0, 0, 0, 0.2);
}

.calculator-screen {
  width: 100%;
  height: 100px;
  border: none;
  background-color: #252525;
  color: white;
  text-align: right;
  padding: 10px 20px;
  font-size: 2.5rem;
}

.calculator-keys {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 10px;
  padding: 20px;
  background-color: #f1f3f6;
}

button {
  height: 60px;
  border-radius: 5px;
  border: none;
  font-size: 1.5rem;
  color: white;
  background-color: #333;
  cursor: pointer;
  transition: background-color 0.2s ease;
}

button:hover {
  background-color: #555;
}

.operator {
  background-color: #f39c12;
}

.operator:hover {
  background-color: #d87a0d;
}

.equal-sign {
  height: calc(80px + 10px);
  grid-column: span 4;
  font-size: 30px;
}

.all-clear {
  background-color: #e74c3c;
}

.all-clear:hover {
  background-color: #c0392b;
}

.decimal {
  background-color: #9b59b6;
}

.decimal:hover {
  background-color: #8e44ad;
}