Nav is working for me, can see links on hover. Try changing link colour.

Hahaha. Too many hours on this dang site!

Umm. could I change the background instead? If not, then my site CSS would need to change.

Also, they're showing up in the preview for sub-pages, but not for my mobile device...

yes, this seems to be a major bug, -still unsolved...
dropdown navigation on touch devices (iphone/ipad) is not working in elemental theme.
older thread:
https://www.concrete5.org/community/forums/5-7-discussion/elemental-...

Thanks for that information, but that doesn't really address my concerns.

Should I choose another theme, or is there a way to change the background color for the dropdown of the menu on mobile?

Got it working by modifying the mobile css in the update folder through

/updates/concrete5.7.5.13_remote_updater/concrete/themes/elemental/css/build/mobile/navigation.less

And changed the from "white" to "black" for the background of the mobile navigation:

.ccm-responsive-overlay {
background: black;
display: none;
position: absolute;
border-bottom: 5px solid @header-site-title-type-color;
width: 100%;
z-index: 99;
top: 120px;
left: 0px;
padding-top: 15px;
padding-left: 20px;
-webkit-text-size-adjust: none;
ul {

You shouldn't really be creating your site using the elemental theme, you should install the Cloneamental theme and modify that instead.
https://www.concrete5.org/marketplace/themes/cloneamental...
Otherwise when you upgrade concrete, you will lose all the modifications you have made to your elemental theme.