Why is this happening w/o a class assigned?

I wanted to create a separate hero home page w/background for XS view using 3.2.4. I duplicated the original bloc and could not get the image to fit correctly. To get back to my starting point I deleted the bloc but I deleted the wrong bloc losing the menu etc. Unfortunately I saved the project and had to recreate the bloc

When I created a new hero page home page the background for the drop down menu was white. I assumed that I could look at the other pages to see what class i used to change the background color. All the other pages DD menus worked correctly (background, hover and active link colors). However none of them had a custom class or sub class or anything assigned, yet they worked.

When i created the new menu the hover and active link colors worked without any classes assigned not the background color.

I cannot understand how this is possible?