It's there to remove the gradient applied by Bootstrap 3 theme styling, which looks terrible with the canvas display. The default background color of the navbar is also #f8f8f8 and not #ffffff and doesn't fit with the rest of the canvas design. It'll be removed when we change to Bootstrap 4 as the theme styling is gone in Bootstrap 4 and there's more helper classes we'll be able to utilize.

For now you'll need to add custom CSS if you want to restyle some parts of the canvas layout, which you can do using CBs CSS override functionality below.

www.joomlapolis.com/blog/kyle/18711-template-css-overrides-made-easy