line break in top navi without background color

Hey Tilman,
First ensure that you have enabled the custom class option for menu items in the Screen Options
Then wrap the second word in your menu item with a span and the custom class line-break like this:

Allgemeinmedizin /<span class="line-break">Naturheilkunde</span>

and add the custom class line-break-item to the menu item:

Then add this CSS to your Enfold Theme Options ▸ General Styling ▸ Quick CSS field:

#avia-menu .line-break-item a {
	line-height: 40px;
	transform: translateY(18%);
}
.line-break-item .line-break {
    display: block;
	line-height: 0px;
}

Now the menu item will be two lines and centered:

I was testing with the default settings for the 2017 Demo, since your settings may be a little different you can adjust the CSS to place the menu text where you wish, if you have trouble link to your page with an admin login so we can assist.

Best regards,
Mike