As a backend developer, I am mainly concerned to make sure that the plugin works with the standard themes released by WordPress, i.e. twentyseventeen, twentynineteen, etc. This ensures maximum compatibility with most themes.
Occasionally you can come across a theme that is not compatible with this plugin. Usually it is a problem of one or two CSS rules and it is possible to fix the issue. If you are using a theme whose CSS rules you believe are interfering with the UIs, let me know because I might be able to help. All that’s usually needed is to inspect the elements with your browser, find out the rule that’s causing the problem, see which of the plugin’s rules it’s hiding, and overwrite that with another rule.
Additionally, perhaps other users can recommend themes that they have had success with.