Clean up "jBar" styling for dropdown header

Picking up some trivial odds and ends to warm up a bit and get my head around the project:

- Fix scrolling issues with dropdown banner (currently "We're recruiting for a volunteer CTO!") and the awkward scrolling of the body elements 'through' it. 
- Tweaked output on mobile to be a bit more visually appealing.

More to come!

(Apologies for the lack of screenshots on this one, having some VirtualBox issues - will attach when fixed)