Question [Q] Android themes without a Launcher APP

Hi every one I've been trying to find themes for my G fit that don't need a launcher app, but I couldn't find any, so I was wondering do I have to install a launcher app to install themes?? I also want to design my own themes.

PS: my phone isn't rooted, nor have I changed anything in it since I bought it in 2012, I have tried rooting it, but I failed.