Since the most recent version of TST, the author has added a barebones style, which can be customized at-will thanks to the custom styles textarea in the addon's settings. I've fired up the Browser Toolbox to get all the correct CSS selectors and then customized things to my liking. I've shared a gist on the addon's github issues with a version of my custom styles. I've since added a few things. I could create a new gist if you are interested