The font size (in pixels) used to generate the image.
If FLIRStyle.inheritStyle is set the CSS font size will be used. This means you can use a style like <h1 style="font-size: 36px;"></h1> and have it work. You can also use points (18pt) instead of pixels and it will be accuretly converted to pixels specific to the users display settings. At this time EMs and % is not supported.