I posted in this thread, what i did is type without any breaks and made it a long string and the container stretched
https://mangadex.org/thread/11559/81/#post_627747
Edit: I'm using Chrome Version 73.0.3683.103 if you needed to know
If you apply that to what I had done, they you can takover all but the left side of the page (where avatars are) and the nav bar at the top.
From my tests, I don't think its possible. But, If anyone know a way to make the text expand leftwards. Then we have the ability to do a complete thread takeover. at least, complete visible page takeover. post button and stuff just moves over to the right and can be found by horizontal scrolling. So, minus the extra takover of thread page buttons, not much more is lost in functionality
Before:
This is a dead deleted chapter thread, which I am using for bbcode testing
Wait, this is a bug? Ive seen this thing for a while and thought it was just how they choose to make it.
I usually see this when im reading mangadex on mobile. Only very occasionally on browser.