If you look at the timeline for a post, e.g. https://meta.stackexchange.com/posts/248289/timeline, you see stuff like this:

![][1]

There is no space between "by" and the username "masegaloeh". 

This isn't a CSS issue; the space is absent in the HTML.

  [1]: https://i.sstatic.net/mfv8F.png