The branding buttons at the footer of every page should be in SVG or at least use a higher-resolution image for HiDPI screens.
SVG versions of the "a Wikimedia project" and "Powered by MediaWiki" buttons are already available at Commons:
[[File:A Wikimedia project.svg]] (copyright by Wikimedia)
[[File:Powered by MediaWiki.svg]] (PD; text might be too light)
Version: 1.23.0
Severity: enhancement