With Frontity, you can build your own theme from scratch matching all your needs or use a ready-to-use one, which will make it much easier. You can even install a starter theme and keep working on top of that.
Basically it's the same as WordPress, just keep working as you usually do.
You can find all the Frontity themes looking for the tag
frontity-theme at npm, but these are the current themes available for your Frontity project, explained in detail:
Frontity Starter Theme by Alexandra Spalato:
Frontity Chakra Theme by Segun Adebayo:
Twenty Nineteen Frontity Theme by Imran Sayed and Smit Patadiya: