[FIX] website_slides: slide in fullscreen needs to have the navbar

Display a slide, enter fullscreen mode
Make the navigation bar appear.

Now, try to push on any button of the nav bar

Before this commit, none of the button work
This is because the fullscreen mode is handled by the browser, and won't let any non-fullscreen
elements be interactive

After this commit, the nav bar is part of the element that are in fullscreen
And the button work

OPW 1839503
closes #24522