body{
  margin:0;
  display:flex;
  justify-content:center;
  align-items:center;
  height: 100vh;
  background-color: hsl(0, 0%, 95%);
}
#calculator {
  font-family: Arial, sans-serif;
  background-color: hsl(0, 0%, 15%);
  border-radius: 15px;
  max-width:500px;
  overflow: hidden;
  border:none;
}
#display{
  width:100%;
  padding: 30px;
  border:none;
  font-size:5rem;
  background-color:hsl(0, 0%, 20%);
  color: white;
  text-align: left;
}
#keys{
  display:grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 10px;
  padding: 25px;
}
.operator-btn{
  background-color: hsl(39, 100%, 50%);
}
button{
  width:100px;
  height:100px;
  border-radius: 50px;
  border:none;
  background-color: hsl(0, 0%, 30%);
  color: white;
  font-size: 3rem;
  font-weight: bold;
  cursor: pointer;
}
button:hover{
  background-color: hsl(0, 0%, 40%);
}
button:active{
  background-color: hsl(0, 0%, 60%);
}
.operator-btn:hover{
  background-color: hsl(39, 100%, 60%);
}
.operator-btn:active{
  background-color: hsl(39, 100%, 80%);
}