Very nice!
Maybe for the long-term future you could look into how to make better use of vertical space. Currently, there are 7 (5 in fullscreen mode)= different sections from content to top of the page. Maybe a compact mode would be nice or less space for content headlines.

Hover over the border (I would suggest to use the full screen, i.e. maximize)

Yes you can drag it in the UI :) it's a new feature in v1