Only colorize project folder in tree view

[ProLoser]

Instead of colorizing the entire tab bar (which looks incorrect for material ui - #7) why not simply colorize the project folder name at the top of the tree view? Maybe an alternative toggle or something?

[long-lazuli]

I made a PR to allow you to use a CSS custom property anywhere in your user-style.
See #9

[FossPrime]

For me just the top of the project isn't enough, as expanded any project could easly out size my screen... and two of the projects use the same framework and have similar names for files... making things very confusing sometimes.