to improve speed of loading and bump up lighthouse score

also fix header that was wrong.
add styles for titles with backlink.
& other changes (see diff, i'm lazy)

also snippet that makes art menu is now separated as mixin (very
powerful thing, btw).

i think that the pictures are just placeholders now. i will try to
improve this 'gallery' a bit later.

also, header is now fixed with transparent background.

maybe i'll replace it with svg later.

and fix some links in site data to make it work.
it's kinda subtle yet, maybe change it later.

add logo and fix overall look