simple CSS tweak: adjust tab bar scrollbar color for dark theme

[TheWebTech]

HubSpot updated their tab bar scrollbar color, we need to override that color to be the brighter blue color again as their change makes the bar hard to see in the dark theme.

file to add css to is https://github.com/williamspiro/HubSpot-Developer-Extension/blob/master/hsDarkIde.css

[danaholdt]

@TheWebTech Added a simple color fix here: #178

This should play nicely with request for the height change.