style.css

*{
    padding: 0;
    margin: 0;
    box-sizing: border-box;
}
.container{
    width: 100%;
    height: 100vh;
    background-color: aquamarine;
    display: flex;
    align-items: center;
    justify-content: center;
}
.calculator{
    background: black;
    padding: 25px;
    border-radius: 10px;
}
form input{
    width: 60px;
    height: 60px;
    outline: 0;
    border: 0;
    border-radius: 10px;
    background: transparent;
    box-shadow: -10px -10px 15px rgba(255, 255, 255, 0.1),5px 5px 15px rgba(0, 0, 0, 0.2);
    font-size: 20px;
    color: white;
    cursor: pointer;
    margin: 10px;
}
#display{
    display: flex;
    justify-content: flex-end;
    margin: 20px 0;
}
#display input{
    text-align: right;
    flex: 1;
    font-size: 45px;
    box-shadow: none;
}
#equal{
    width: 145px;
}
.footer{
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 10px auto;
    
}
.footer{
    color:chocolate;
    padding-top: 10px;
    font-family:Arial, Helvetica, sans-serif;
}