Once you've added a theme to your board, it cannot be deleted. You can only enable or disable a theme. Also, perhaps the 'Delete Theme' link should be a little further away from the other theme options.

Hey, thanks for pointing this out! I notice the links in that area are not well formatted anyway.

I'll add it to my GitHub issues and report back here once it has been resolved.

Just a heads up that I've made a deployment that makes this possible now.

I'll revisit the theme listing interface again at some point to improve buttons / layout