style.css

*{
    margin: 0;
    padding: 0;
    font-family: 'poppins', sans-serif;
    box-sizing: border-box;

}

.container{
    width: 100%;
    height: 70vh;
    background:#e3f9ff;
    display:flex;
    align-content: center;
    justify-content: center;


}

.calculator{
    background:#3a4452;
    padding: 20px;
    border-radius: 10px;
}

.calculator form input{
    border: 0;
    outline: 0;
    width: 60px;
    height: 60px;
    border-radius: 10px;
    box-shadow:-8px -8px 15px rgba(255, 255, 255, 0.1),5px 5px 15px rgba(0, 0, 0, 0.2);
    background: transparent;
    font-size: 20px;
    color:#fff;
    cursor: pointer;
    margin: 10px;
}

form .display{
    display:flex;
    justify-content: flex-end;
    margin:20px 0;

}

form .display input{
    text-align:right;
    flex:1;
    font-size:45px;
    box-shadow: none;
}

form input.equal{
    width: 145px;

}

form input.operator{
    color:#33ffd8;

}