Enhance headerbar theming

[PlantLily]

It appears that mint 21 got rid of metacity, with that go the borders... Is it possible to reimplement the window borders in gtk3?

Also due to metacity no longer drawing the title bar the sheen on the titlebar corners is now cut off weirdly by the rounding

[Elbullazul]

hi, sorry for the delay

I don't think you can make metacity window decorations work again. Headerbars should already themed.

titlebar corners [...] cut off weirdly by the rounding

Headerbar theming hasn't been touched in a while, so it could do with some improvements. I already have an idea on how to fix this, but I can't say when it's going to be implemented.

[Septicity]

Maybe this can be accomplished with border-image? Or does that work differently in GTK CSS?