Евгений

.box {
    background: blue;
    width: 50px;
    height: 50px;
    position: relative;
}

<meta name="viewport" content="width=device-width, initial-scale=1.0">

$('.responsive-menu-items > ul > li').each(function () {
        let el = $(this),
            link = $('> a', el),
            ul = $('> ul', el);
        if (ul.length && window.matchMedia("(max-width: 400px)").matches) {
            link.click(function () {
                ul.toggleClass('subcategories');
                return false;
            })
        }
    })

var countDownDate = new Date(time.replace(' ', 'T')).getTime();
   if (isNaN(countDownDate)) {
      countDownDate = new Date(time).getTime();
   }