style.css

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

.container{
    width: 100%;
    height: 100vh;
    background: #b4ffd3;
    display: flex;
    align-items: center;
    justify-content: center;
}

.calculator{
    background: #25473f;
    padding: 20px;
    border-radius: 15px;
    
}

.calculator form input{
    border: 0;
    outline: 0;
    width: 60px;
    height: 60px;
    border-radius: 10px;
    box-shadow: -8px -8px 15px #172e24 , 5px 5px 15px #172e24;
    background: transparent;
    font-size: 33px;
    color: rgb(255, 255, 255);
    cursor: pointer;
    margin: 10px;
}

form .display{
    display: flex;
    justify-content: flex-end;
    margin: 20px 0;
    border-radius: 10px;
    background-color: rgb(255, 255, 255);
}

form .intro{
    display: flex;
    justify-content: center;
    margin: auto;
    background-color: #29af90;
    border-radius: 10px;
}

form .intro input{
    color: #172e24;
    text-align: center;
    flex: 1;
    font-family: Impact, Haettenschweiler, 'Arial Narrow Bold', sans-serif;
    font-size: 26px;
    box-shadow: none;
}

form .display input{
    color: #172e24;
    text-align: right;
    flex: 1;
    font-size: 45px;
    box-shadow: none;
}

form input.equal{
    font-size: 44px;
    width: 145px;
    background-color: #29af90;
    color: rgb(54, 54, 54);
}

form input.operator{
    color: #3aff5b;
}