style.css

body {
  display: flex;
  justify-content: center;
  background-color: #97d9e1;
}

.frame {
  font-size: 24px;
  background-color: white;
  max-width: 500px;
  border-radius: 20px;
  padding: 2%;
  margin: 40px 20px 20px 20px;
}

button {
  color: white;
  border-radius: 10px;
  width: 50px;
  height: 50px;
  border: none;
  margin: 5px 5px;
  box-shadow: 3px 3px 3px #cccccc;
  font-size: 30px;
  background-color: #3f4557;
}

button:active {
  color: #f484a2;
}

button:focus {
  outline: 0;
}

button:hover {
  background: linear-gradient(145deg, #6e66f2, #f484a2);
}

.top {
  flex-direction: row;
  display: flex;
  justify-content: center;
}

.functionbox {
  display: inline-block;
}

output {
  font-size: 20px;
  padding: 5px 8px;
  color: white;
  border-radius: 8px;
  width: 180px;
  height: 26px;
  display: block;
  background-color: #f484a2;
  margin-top: 12px;
  margin-bottom: 20px;
  box-shadow: 1px 2px 2px #b7c0c4;
}

.buttonclear {
  margin-right: 10px;
  margin-left: 0;
  border-radius: 50px;
}

.operator {
  background-color: #6e66f2;
}

@media screen and (min-width: 700px) {
  button {
    width: 90px;
    height: 90px;
  }
  output {
    width: 300px;
    height: 60px;
    margin-top: 20px;
    font-size: 40px;
  }
}