body{
  font-family: 'open sans' ,sans-serif;
  background-color: black;
}
#container{
  width: 1000px;
  height: 615px;
  background-image: linear-gradient(rgba(0, 0, 0, 0.3),rgba(0, 0, 0, 0.5)), url(yash.jpg);
  margin:  20px auto;
}
#Calculator{
  width: 350px;
  height: 560px;
  background-color: orange;
  margin: 0px auto;
  position: relative;
  top: 20px;
  border-radius: 5px;

}
#result{
height: 120px;
}
#key{
  height: 400px;
}
#history{
  text-align: right;
  height: 20px;
  margin: 0 20px;
  padding-top: 20px;
  font-size: 17px;
  color: red;
}
#output{
  text-align: right;
  height: 60px;
  margin: 10px 20px;

  font-size: 20px;
}
.operator, .number, .empty{
width: 50px;
height: 50px;
margin: 18px;
float: right;
border-radius: 30%;
font-size: 17px;
font-weight: bold;
}
.number, .operator{
  cursor: pointer;
}
button:nth-child(4){
  font-size: 20px;
  background-color: Green;
}
button:nth-child(8){
  font-size: 20px;
  background-color: yellow;
}button:nth-child(12){
  font-size: 20px;
  background-color: red;
}button:nth-child(16){
  font-size: 20px;
  background-color: aqua;
}button:nth-child(20){
  font-size: 20 px;
  background-color: orange;
}