Bugs in the new site interface

The forum is a "sticker" on some kind of "background". The option to disable the background has appeared, but it still takes up space on the screen (as empty space). Could you make it so that when the background is disabled, the message field "stretches" across the entire screen, like in the mobile version? I just don't like "mobile versions", and even on my phone I always view sites "in PC mode". So it turns out that part of the screen here is "wasted"...