body 
{
    padding: 0;
    margin: 0;
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    user-select: none;
    background: url(background.jpg) no-repeat; 
    background-size: cover;
    background-position: center;
}

.container
{
    margin-left: 1.8em;
    padding: 20px;
    border-radius: 8px;
    box-shadow: 13px 13px 20px #cbced1,
            -13px -13px 20px #ffffff;
}

.display #screen
{
    margin-bottom: .5em;
    width: auto;
    height: 70px;
    font-size: 35px;
    outline: none;
    border: none;
    text-align: right;
    padding-right: .5em;
    background: #ecf0f3;
    border-radius: 6px;
    box-shadow: inset 8px 8px 8px #cbced1,
                inset -8px -8px 8px #ffffff;
}

.buttons 
{
    width: 100%;
    margin-top: 1.7em;
    display: flex;
    justify-content: center;
    align-items: center;
    flex-direction: column;
}

.buttons .row button
{
    width: 60px;
    height: 30px;
    font-size: 16px;
    border: none;
    outline: none;
    margin: 5px;
    border-radius: 4px;
    transition: .1s;
    box-shadow: 5px 5px 8px #00000020,
                -5px -5px 8px #ffffff;          
}

.buttons .row button:hover
{
    box-shadow: inset 5px 5px 8px rgba(16,16,16,.1)
                inset -5px -5px 8px #fff;
    background: #fff;
}

#eval
{
    background: #33ccff;
    color: #fff;
    box-shadow: inset 5px 5px 8px #66d9ff,
                inset -5px -5px 8px #00ace6;
}

#eval:hover
{
    box-shadow: inset 5px 5px 8px #00ace6,
                inset -5px -5px 8px #00ace6;
}

#ac
{
    background: #33cc33;
    color: #fff;
}

#ac:hover
{
    box-shadow: inset 5px 5px 8px #2eb82e,
                inset -5px -5px 8px #33cc33;
}

#ce
{
    background: #ff3399;
    color: #fff;
}

#ce:hover
{
    box-shadow: inset 5px 5px 8px #e60073,
                inset -5px -5px 8px #ff3399;
}

/* for smaller screens */
@media screen and (max-width: 360px) { 
    .container {
        margin-left: 0; 
        border-radius: 0; 
        box-shadow: none; 
        padding: 10px; 
    }

    .buttons .row button {
        width: 40px; 
        height: 25px; 
        font-size: 14px; 
    }

    .display #screen {
        font-size: 24px;
        height: 50px;
    }
}