Trouble formatting closed captions in my video

Hi all,

I'm "new" to closed captions of my videos, but have most things up and running. I create videos in Camtasia, export the SRT file (CC file format Camtasia supports). I convert SRT to WebVTT format which Rise supports. The "default" font format, size, anchor position (centered, bottom)... all good. BUT sometimes I need to format the text. Some embedded HTML tags work (italics, bold), but when I try to change the font size, both HTML and various attempts at CSS w/in the WebVTT file all fail. Is this supported? I'd like to be able to change the font on all cues w/in the VTT file, OR on some individual captions. (For example, if the captions become invasive on some diagrams or application demonstrations.) This works as a test: <c.yellow.bg_blue.magenta.bg_black>Text color changes here</c>

But this (and other tests all fail on the font size): <c.font-size.xx-small>
Font size does not change here . </c> 

I've tried it with font-size 12px, 12pt, ... 

Has anybody run into this? If so, what is the exact syntax that worked for you?