Closes https://github.com/ppy/osu/issues/28750.
Yes this is not the perfect change to fix this (which would probably be
some framework change to take bounds of the parenting input manager into
account). I really do not want to go there and would like to just fix
this locally and move on. Due to the game-wide scaling container this
sorta works for any resolution anyhow.
The +2 for the top isn't really needed for the original purpose as content fades out now, but visually, having the header and content spacing looks more correct.