[BUG-6553] Ignition Perspective Drop Down search text color left out of style sheet

I don't like css inject, but yes you can

or you can create your own css theme, see readme file in data\modules\com.inductiveautomation.perspective\themes
or you can wait 8.1.22 release wich give you a project style in designer:
https://forum.inductiveautomation.com/t/new-stylesheet-resource/64787