Thank you for feedback. Be aware that this style is still not finished, and there are many fixes to be implemented yet, including fixes for bugs u pointed out and some that u still didn't found 😆.
About js, js is implemented in custom header, which works independently from js that flarum is using. Error about js u saw is, i assume, because of way i wrote a js script. As it first check if some app. is undefinied etc. No need to concern yourself with it, as it will not affect a usability and user experience in any way.