Shadow Around Header

Hello. I am trying to add a shadow under the main mobile menu header and possible around the left menu too. The menu background is white and so is the page on my site and I want the shadow to show a separation between the header/menu and the site content.

I saw you had a similar code posted in another Topic but I copied this code into the custom CSS section in the plugin settings. I still don’t get any shadows: What could I be missing?

.mob-menu-slideout, .mobmenu-push-wrap, .mob-menu-slideout, .mob-menu-header-holder {
box-shadow: 12px 12px 12px 12px;
}