CSS: How to find out what makes my navi disappear?

Your theme’s vendors would be best to ask.

It’s my own theme.

Make sure you are not using some of the responsive classes from Bootstrap that are hiding your content, like ,hidden-tablet, ,visible-phone, ....

https://getbootstrap.com/2.3.2/scaffolding.html#responsive

@raider000 a link to your theme/website will make it easier to help.

Thank you.

I needed to add the following:

@media (max-width: 979px) and (min-width: 768px) {
	.nav-collapse.collapse { height: auto; }
}

It works now! ??