Hi Attila,
You’re on the right track with regards to setting up the sub-menu. The sub-menu just has its font color the same as its background color which is why it seems like the menu items are missing.
With that said, can you try adding this custom CSS and see how it goes?:
li.menu-item ul.sub-menu li.menu-item a {
color: var(--contrast);
}
—contrast is the contrast color set in your Global colors in Appearance > Customize > Colors. You can modify this value to your preference. You may also use something like rgb(0, 0, 0) as the value.
See this for reference: https://share.getcloudapp.com/z8ukWzXB
How this helps! 🙂