@media (width >= 800px) {
    #middle {
        margin: 1em auto;
        max-width: 1200px;
        display: flex;
        gap: 1em;
        justify-content: center;
    }

    #settings {
        flex: 0 1 20em;
    }

    #output {
        flex: 1 0 0;
    }
}

@media (width < 800px) {
    #settings,
    #output {
        margin: 0.75em;
    }
}