I've build a Gantry 5 (Helium theme) website for a cycling club. Site is ok on Firefox, Chrome and Android telephone. Only Safari on Ipad is giving some trouble, Safari on Imac not checked. When you select a submenu, the submenu disappears behind the photo slider. The photoslider is just below the menu position. I tried to do someting with Z-index in custom.css (override file) without any result. See code below
.g-main-nav .g-sublevel > li > .g-menu-item-container {
z-index: 10000;
}
The Joomla version is 3.9.23 and teh Helium version is 5.4.36
Check the website
[here /url]