From volunteer andrybak on Wikipedia:VillagePump:

I don't know how the community feels about pixel peeping in UI elements, but here's a very minor nitpick about rendering of some of the notification icons (Commons category). They are originally 20x20 pixels SVG files. In the notifications UI they are rendered in size 30x30 pixels. Positions of some vertical and horizontal edges in these icons relate to the size 30x30 in such a way, that some edges are blurred. The size 30x30 pixels is set through the following CSS rule, which is independent of the skin (Cologne Blue · MinervaNeue (mobile) · Modern · MonoBook · Timeless · Vector):