Images using the code [[File:Flag of Japan.svg|30px|border]] are expected to have a 1px grey border.
But this border is missing in the Timeless skin.
Demo: https://en.wikipedia.org/w/index.php?title=Draft:Sandbox&oldid=817291472&useskin=timeless
Expected: https://en.wikipedia.org/w/index.php?title=Draft:Sandbox&oldid=817291472&useskin=vector
Indeed, it is missing the following rule from mediawiki.skinning/content.css (module mediawiki.skinning.interface):
img.thumbborder { border: 1px solid #eaecf0; }