Yes, you can reference the system properties in your CSS. I know this works well with colors, not sure about fonts.
Just need to reference like this:
<style type="text/css">
body {
font-family: InfoText; /* Tahoma, Segoe UI or MS Sans Serif */
color: ButtonText;
background-color: ButtonFace;
}
</style>
EDIT: With a little more thought, I think this will work with fonts as well, but not how you were referencing it with dialog-font. You would just reference the system property, same as the other two, and the font defined for that property will be referenced.
Second EDIT: Here is a blog with the list of available properties, as well as more info than I had on fonts:
How to Use Operating System Styles in CSS