.calculator {
  width: 200px;
  margin: 0 auto;
  text-align: center;
}

.header {
  display: flex;
  justify-content: space-between;
}

.title-left, .title-right {
  color: cyan;
}

#display {
  width: 100%;
  height: 40px;
  margin-bottom: 10px;
}

.keys {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 5px;
}

button {
  width: 100%;
  height: 40px;
  font-size: 20px;
}