Make scroll bar for accounts in catch-up taller, give it more whitespace, and do not fade it out.

[tuxwise]

Is your feature request related to a problem? Please describe.
The scroll bar for accounts in the catch-up window is quite flat, crammed between other interactive elements and fades out.

Describe the solution you'd like
Make the scroll bar taller, give it more whitespace above and below, and do not fade it out.

Describe alternatives you've considered
The scroll bar is the only means to navigate the account avatars ribbon. Another option might be to optionally show a block of all avatars, with appropriate line breaks.

Additional context