Masking Externally loaded CSS text (from.txt file)

Well, I know how to do it when using dynamic text and using setmask and embedding your fonts, but how do you do it when you are using a CSS font class with 3 diff. fonts and maybe even more?

There is no mention of how to use a mask over a dynamic textfield in the MX 2004 tutorial with externally loaded CSS .txt file, so hopefully someone knows how to do this? I am getting a blank text field, but it works when I delete the mask layer.