Try the following:
- Create a new HTML item in Freeway Pro and type the text "Hello World!" inside it.
- Select the text and in the Styles Inspector (the fourth pane of the Inspector palette) click the + to the right of Text and select New to open the Edit Styles dialog.
- Don't worry about the name of the style for now. Click the Extended button and in the dialog that appears click the New button.
- In the dialog that appears type border-bottom in the Name field and 1px dotted black in the Value field and click Ok and Ok again.
- You won't see anything in the Freeway view since this is an extension of something that Freeway doesn't know about, to see the change click Preview or the Preview in Browser toolbar button.