www.wysiwygwebbuilder.com

I just installed WWB 18 and couldn't find an option to save different styles in the CSS menu.
Does this possibility exist?

There is no option to save styles in the CSS menu.
But you can copy/paste the entire object, if you want to reuse the same style.

The problem is that I have several hundred CSS menus in my site, and if I want to make a style modification in these menus it can take me hours, and the possibility of forgetting some menus.

Note that you can use global styles (classes) in the CSS menu.

https://wysiwygwebbuilder.com/support/wb18tryouts/wb18_styles_navigation.html

When using "global styles", the font size parameters do not work.
The only parameters that work are the background parameters and text colors.
The other parameters (like "Layout - Main menu") are not included in the "styles".
So the "class" are not really usable.