* {
  box-sizing: border-box;
  margin: 0;
}
.calculator {
  background-color: #f2f2f2;
  padding: 20px;
  max-width: 400px;
  margin: 0 auto;
  border: solid 1px #ccc;
  box-shadow: 0 2px 5px rgba(0, 0, 0, 0.3);
  border-radius: 5px;
  margin-top: 40px;
}
#result {
  width: 100%;
  padding: 20px;
  font-size: 24px;
  border: none;
  box-shadow: 0 2px 5px rgba(0, 0, 0, 0.3) inset;
  border-radius: 5px;
}
.buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  grid-gap: 10px;
  margin-top: 20px;
}
button {
  padding: 10px;
  font-size: 24px;
  border: none;
  box-shadow: 0 2px 5px rgba(0, 0, 0, 0.3);
  border-radius: 5px;
  cursor: pointer;
  transition: background-color 0.3s ease;
}
button:hover {
  background-color: #ddd;
}
.clear {
  background-color: #ff4136;
  color: #fff;
}
.number & .number {
  background-color: #fff;
  color: #333;
}
.operator {
  background-color: #0074d9;
  color: #fff;
}
.equals {
  background-color: #01ff70;
  grid-row: span 3;
  color: #fff;
}