"font-family: monospace, monospace"
You are right. The font-family: monospace, monospace;
declaration is a simple hack/workaround for some browsers which tend to reduce the font size of monospace fonts.
More info on this Github issue: https://github.com/necolas/normalize.css/issues/519#issuecomment-197131966
Yes, this is a workaround for a long-standing (I'm talking over a decade) issue with browsers' handling of the monospace
generic family. Eric Meyer has a detailed write-up on this, and I explored this recently while answering this question that's specifically about Firefox's handling of monospace fonts.
Why does it work? How is monospace, monospace
different to just monospace
? Nobody knows. I made a guess based on Firefox's behavior, but it's just that: a guess. But one thing is clear: monospace, monospace
is recommended over just monospace
if you don't want to deal with this behavior.