* {
  box-sizing: border-box;
}
p {
  -webkit-margin-before: .2em;
  -webkit-margin-after: .2em;
}
.whole-page {
  width: 320px;
  background-color: royalblue;
  margin: auto;
  padding: 5px;
}
.screen {
  width: 310px;
  height: 50px;
  border: blue solid 2px;
  border-radius: 5px;
  margin: 5px auto;
  padding: 5px;
}
.buttons {
  width: 310px;
  border: blue solid 2px;
  border-radius: 5px;
  margin: 5px auto;
  padding: 5px;
}
.zero-button,
.one-button,
.two-button,
.three-button,
.four-button,
.five-button,
.six-button,
.seven-button,
.eight-button,
.nine-button,
.plus-button,
.minus-button,
.multiply-button,
.divide-button,
.decimal-button,
.equals-button {
  width: 64px;
  height: 64px;
  display: inline-block;
  border: blue solid 2px;
  border-radius: 5px;
  box-shadow: 3px 3px 3px navy;
  margin: 3px;
  padding: 5px 25px 0 20px;
  font-size: 36px;
  text-align: center;
}
.plus-button,
.minus-button,
.multiply-button,
.divide-button,
.equals-button {
  background-color: mediumseagreen;
}