style.css

:root {
    --color-1: #425F57;
    --color-2: #749F82;
    --color-3: #A8E890;
    --color-4: #CFFF8D;
}

* {
    margin: 0;
    padding: 0;
}

html, body {
    background: var(--color-1);
    text-align: center;
    direction: rtl;
}

#content {
    width: 50vw;
    margin: 25vh auto;
}

#content > input#uin {
    background: var(--color-4);
    width: 40vw;
    /* color: var(--color-2); */
    padding: 1rem;
    font-size: 1rem;
    direction: rtl;
}

h1#out {
    color: var(--color-4);
    font-size: 3rem;
}

button#btn {
    background: var(--color-3);
    padding: 1rem;
    font-size: 1rem;
}

footer {
    background: black;
    color: white;
    text-align: center;
    padding: 1rem 0;
    position: fixed;
    bottom: 0;
    width: 100%;
}

@media only screen and (max-width: 600px) {
    #content {
        width: 90vw;
    }
    #content > input#uin {
        width: 80vw;
    }
    button#btn {
        width: 87.5vw;
    }
}