the h1 underline does not extend full width of wikibase-entityview-main.
It could be that this is somehow intended (?) and maybe I can be convinced...
Otherwise, I think it should be full width like we have currently on Wikidata (and wikipedia), until time that redesign has header fully like the mockup: https://www.wikidata.org/wiki/Wikidata:UI_redesign_input#Mockups