*, *::before, *::after {
  box-sizing: border-box;
  font-family: Arial, sans-serif;
}
body {
  padding: 0;
  margin: 0;
  background: linear-gradient(to right, #00AAFF, #00FF6C);
}
.calculator {
  background-color: #263238;
  display: inline-block;
  width: 100vw;
  height: 100vh;
}
.calculator > .stack {
  height: 50%;
}
.calculator > .stack > div {
  border-bottom: 1px solid #455A64;
  height: 16.6666666%;
  color: white;
  font-size: 3rem;
  display: flex;
  justify-content: right;
  align-items: center;
  padding-right: 0.5rem;
}
.calculator > .buttons {
  display: grid;
  grid-template-columns: repeat(5, 20%);
  grid-template-rows: repeat(5, 20%);
  grid-gap: 0;
  height: 50%;
}
.calculator > .buttons > button {
  border: 1px solid #263238;
  background-color: #37474F;
  color: white;
  font-size: 2rem;
  outline: none;
  border-radius: 5px;
}
.calculator > .buttons > button:active {
  background-color: #263238;
}
.calculator > .buttons > button.operator {
  background-color: #4CAF50;
}
.calculator > .buttons > button.operator:active {
  background-color: #388E3C;
}
.calculator > .buttons > button.enter {
  background-color: #FF9800;
  grid-column: span 2;
}
.calculator > .buttons > button.enter:active {
  background-color: #F57C00;
}
.calculator > .buttons > button.backspace {
  background-color: #F44336;
}
.calculator > .buttons > button.backspace:active {
  background-color: #D32F2F;
}