d0 = new Date('May 28, 2019'); // пуск сайта
d1 = new Date();
dt = Math.round((d1.getTime() - d0.getTime()) / (1000*60*60*24));
function declOfNum(number, titles) {
cases = [2, 0, 1, 1, 1, 2];
return titles[ (number%100>4 && number%100<20)? 2 : cases[(number%10<5)?number%10:5] ];
}
document.write(dt + ' ' + declOfNum(dt, ['день', 'дня', 'дней']));.submenu{
width: 100%;
position: absolute;
margin: 0;
padding: 0;
display: none;
text-align: justify;
}
<meta name="viewport" content="width=device-width, initial-scale=1, viewport-fit=cover">display: flex; justify-content: center; align-items: center;