style.css

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

.container {
  width: 100%;
  height: 100vh;
  background: rgb(131, 58, 180);
  background: linear-gradient(90deg, rgba(131, 58, 180, 1) 0%, rgba(253, 29, 29, 1) 50%, rgba(252, 176, 69, 1) 100%);
  display: flex;
  justify-content: center;
  align-items: center;
  color: white;
}
.calculator{
  width: 300px;
  height: 400px;
  background-color: rgba(255, 255, 255, 0.2);
  display: flex;
  flex-direction: column;
  justify-content: space-around;
  align-items: center;
  font-family: cursive;
  user-select: none;
  border-radius: 10px;
}
.display{
  width: 300px;
  height: 60px;
  display: flex;
  justify-content: center;
  align-items: center;

}
.display > .content{
  width: 260px;
  height: 50px;
  display: flex;
  align-items: center;
  justify-content: flex-start;
  padding: 0px 30px;
  font-size: 18px;
  border-radius: 12px;
  margin-top: 4px;
  background-color: rgba(0 0,0, 0.1);

}
.keys{
  width: 300px;
  height: 330px;
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
}
.keys > .row{
  width: 260px;
  height: 60px;
  display: flex;
  flex-direction: row;
  justify-content: space-evenly;
  align-items: center;
}
.keys > .row > .key{
  width: 60px;
  height: 50px;
  display: flex;
  justify-content: center;
  align-items: center;
  transition: 0.2s;
  border-radius: 12px;
  background-color: rgba(0, 0, 0, 0.1);
  cursor: pointer;
}