I found this when doing a little searching:
There's the special thing about them that in CSS, the colon needs to be
"escaped", usually as \: (i.e., a backslash is written before the
colon). The reason is that the colon is a special character in CSS
syntax in pseudo-class and pseudo-element selectors.
Not sure if that helps any but using a colon in a class name is not something I would ever do.