I like it, only posted from desktop so far.
Not a fan of the H1 title that looks like part of the textarea. I found myself clicking at the end of the title, then pressing ↓ to go to the line below, and it obviously didn’t work.
Large titles can be partially hidden:
On mobile, the toolbar is quite narrow. The way a thumb naturally moves from left to right on a smartphone screen isn’t a straight horizontal line. It’s slightly curved from bottom right top right top, and this effect might be increased if the target area is high on the screen.
This tends to make me miss the sidebar dragging toggle.
I’m not sure how to improve that. Making the toolbar taller seems not the best solution.
Perhaps the detection area could be slightly larger than the toolbar, the same way platform game developers allow the player’s character to jump from or land on an edge even if they are a few pixels too far and should normally fall.