light.css

.calculator {
  border: 4px solid black;
  width: 300px;
  margin: 50px auto;
  padding: 10px;
  background-color: #eee;
  border-radius: 5px;
}
.display {
  width: 100%;
  margin-bottom: 10px;
  background-color: #fff;
  border: 2px solid black;
  border-radius: 4px;
}
.display input[type="text"] {
  width: auto;
  padding: 10px;
  font-size: 20px;
  text-align: right;
  border: none;
  outline: none;
}
.buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  grid-gap: 5px;
}
button {
  background-color: gray;
  color: white;
  padding: 10px;
  border: none;
  border-radius: 4px;
  cursor: pointer;
}
button:hover {
  background-color: dimgray;
}

button:active{
  background-color: black;
}

.dark{
  background-color: aqua;
}

.themes{
  align-items: center;
  display: flex;
  justify-content: center;
}

.themes > button{
  border: 1px solid gray;
  margin: 2px;
  background-color: beige;
  color: gray;
}