style.css

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
}

#calculator {
  display: flex;
  flex-wrap: wrap;
  width: 350px;
  height: 450px;
  color: white;
  background-color: black;
}

#display {
  display: flex;
  align-items: center;
  font-size: 50px;
  background-color: gray;
  width: 350px;
  height: 100px;
  border: 1px solid white;
}

#numbers {
  border: 1px solid;
  display: grid;
  grid-template-columns: 66.6px 66.6px 66.6px;
  align-content: start;
  width: 200px;
  height: 500px;
}

#numbers span {
  text-align: center;
  width: 66.6px;
  height: 66.6px;
  font-size: 40px;
  border: 1px solid white;
}

#functions {
  border: 1px solid;
  width: 150px;
  height: 250px;
  display: grid;
}

#functions span {
  text-align: center;
  border: 1px solid white;
  text-align: center;
  font-size: 40px;
}

#equal-clear {
  width: 140px;
  border: 1px solid white;
}