Icons' margins on the sitediffer on hover 
When hovering over the icons, they generally seem to be a bit closer to the bottom of the area than the top. Some icons, like activitypub look mostly fine, while others like Mastodon are a bit more obvious. Very minor, but it seems like the fix for this could be tied in with the centering and viewbox issues (Merging Font-Awesome-4.7.0 viewBox specifications · Issue #200 )