I haven’t been able to find an answer to this question, but I’m sure there’s a good reason.
All CSS syntax is case-insensitive within the ASCII range (i.e., [a-z] and [A-Z] are equivalent), except for parts that are not under the control of CSS. A long time ago that was not the case (think Netscape 6 ) as well as with XHTML. So it makes sense to avoid confusion and convert. Since spaces would create additional class name webflow throws a hypen in. Good class naming is an art form; lost with most designers.