The design of Pinboard exists in a similar but self hosted service called linkding [1]. I've been self hosting with Docker for a few years with no issues I can recall. Just checked and it does have the responsive forms as well.
One weird thing though is, that Linkding does not have marking a bookmark "read" on first click: This is the most useful feature on Pinboard for me.
Via the pinboard-bookmarklet I pile all the links I come across, then mass read them and can track what's been read because the first click marks them on Pinboard.
Linkding: Settings -> General -> Import "Import bookmarks and tags in the Netscape HTML format. This will execute a sync where new bookmarks are added and existing ones are updated."
The stuff in quotes is verbatim from the admin panels, I have not tried it.