In 1.8.3 Etherpad introduced a new feature called the “Theme variant generator”. To access it append #skinvariantsbuilder to your Pad URL IE http://video.etherpad.com/p/examplethemeshiznee#skinvariantsbuilder
Once you have it styled how you like then copy the Result to settings.json and restart Etherpad. After restart this style will be applied to pads and you don’t need to include the #skinvariantsbuilder.