html, body{
    margin: 0;
    padding: 0;
}
.calculator{
    font-family: "poppins", sans-serif;
    font-optical-sizing: auto;
    font-style: normal;
    margin: auto;
    border: 1px solid black;
    box-shadow: 5px 10px 18px #888888;
    border-radius: 20px;
    padding-left: 50px;
    padding-right: 50px;
    padding-top: 50px;
    padding-bottom: 50px;
    margin-top: 50px;
    width: 350px;
    justify-content: space-between;  
    align-items: center;
    background-color:beige;
}
#heading{
    text-align: center;
    margin-top: 50px;    
    font-size: 40px;
    font-family: "poppins", sans-serif;
    font-optical-sizing: auto;
    font-weight: bold;
    color: darkblue;
}
.buttons{
    display: grid;    
    grid-template-columns: repeat(4, 1fr);
    gap: 4px;
    margin-top: 50px;
    padding: 30px;
    border: 2px solid black;
    background-color: aliceblue;
    border-radius: 30px;
}

.onScreen{
  height: 60px;
  font-size: 2rem;
  font-weight: bold;
  text-align: right;
  padding: 10px;
  border: 2px solid #333;
  border-radius: 10px;
  background-color: whitesmoke;
}


#b0, #b1, #b2, #b3, #b4, #b5, #b6, #b7, #b8, #b9{
    background-color:lightgray;
    height: 50px;
    width: 100px;
    border-radius: 20px;
    font-size: 20px;
    width: 50px;
}

#add, #subtract, #multiply, #divide, #equal, #clear{
    background-color: lightsalmon;
    height: 50px;
    width: 100px;
    border-radius: 20px;
    font-size: 20px;
    width: 50px;
}
#b0:hover, #b1:hover, #b2:hover, #b3:hover, #b4:hover,
#b5:hover, #b6:hover, #b7:hover, #b8:hover, #b9:hover {
  background-color: white;
}
#add:hover, #subtract:hover, #multiply:hover,
#divide:hover, #equal:hover, #clear:hover {
  background-color: tomato;
  color: white;
}