Hey, @mannyo,
How would I increase the font size of individual submenu without doing it for all?
In the example from my previous reply, if you add that bigtextmenu
CSS name class to an individual menu item, only that menu item should be affected by the custom styles. If the styling is being applied to all the items in the menu, it might be the case that you added the CSS class name to the Navigation Block itself (as opposed to a single item). Could you please double-check?
Do I have to create a CSS as you showed above for each particular submenu I want to increase the font size? I’m asking because when I select a particular submenu, I’m not seeing an option to increase font size.
The way the Navigation Block works at the moment, any changes you make will affect all the items in it. In principle, you should be able to adjust the global size of your menu using the typography setting, as seen below:

Would this make sense? Were you referring to this?
the bold works even though I am using the menu from the previous theme. Is that what you mean by converting to regular links?
Not quite. I was referring to converting the “Page List” block to regular individual links in order to be able to add individual CSS class names, as illustrated by this video:
Please let me know if that helps!