function changeMenuState() {
    var menu = document.getElementsByClassName('collapse-nav')[0];
    var cover = document.getElementById('collapse-nav-cover');
    if (menu.style.display == 'none') {
        menu.style.display = 'flex';
        cover.style.display = 'block';
    } else {
        menu.style.display = 'none';
        cover.style.display = 'none';
    }
}

document.getElementById('collapse-nav-cover').style.display = 'none';