fix(html): replace main element with div

[0x-r4bbit]

the <main> element can only be used once per page
this commit fixes it

[cburgdorf]

Hey, thanks for jumping on this. I'm super happy to see mobile support brewing. I think there are a couple of things that need to be addressed before this can be merged:

• while the UI looks much better on mobile now, it seems to introduce some regressions for desktop. The logo seems to be too small and I'm also not a fan of stacking the input boxes vertically on desktop. While it makes sense to place them vertically for small screens, I love the unified box for larger screens.
• please make sure that all css classes are prefixed with sw. Actually sw is kinda deprecated and we should rename everything to ny or ninya or something alike but having classes without a project prefix is a no go.
• you seem to have thrown much stuff into one scss file. While I agree that our current structure feels a bit overly complex, I'm strongly against throwing too many things together in one file.

Otherwise, I really like it!

[0x-r4bbit]

Alright, will update the PR