Allow further resizing of the sidebar

[disassembledd]

Is your feature request related to a problem? Please describe.
Full-screen layout leaves significant dead space in the sidebar that you cannot resize away. This causes the reading content to be pushed to the right half of the screen. It appears a significant minimum is being used

Describe the solution you'd like
Allow the dead space to be resized.

Describe alternatives you've considered
Shrinking the window causes this dead space to resize appropriately.

Additional context
Dead space when full-screened.

Appropriate size when shrunk.

I am unfortunately not a decent enough web dev to submit a PR.