Desktop App Sidebar

I’m using the desktop app of Rocket Chat.
When the windows isn’t enlarged, I’d like to be able to reduce the width of the windows without the sidebar where it shows the contacts to disapear. View picture for better explanation of desire result.
Just by trial and error, I found out that under 780 the sidebar disapear. We think it’s some kind of bootstrap or Jquery code hidden somewhere but we can’t seem to find it.

help please

After looking at the code, we managed to see that there’s an auto generated code for the width.
However, there’s no way of modifying it by accessing the files because they are as read only. Tried looking at the js files which are also read only. Using the dev Tool managed to changed to what we wanted but can’t make it stay. So we tried to copy the modified code from dev tool and add it to the Custom CSS section but to no avail. It still doesn’t work