css: misc changes - anchor links in list elements can now be displayed more obviously using "list__item--show-links" class - specific style for disabled button - adapted form styles to new "select" field - other small changes, see diff

@media (min-width: 500px) {
    #main_area {
        background-image: var(--bg-img);
        background-repeat: no-repeat;
        background-size: cover;
    }
}