Problems with caption styling of the touchkit-navbutton

Hello,

we are developing a small "WebApp", yet using vaadin 6.7.9. and vaadin touchkit 2.1.1.

I'm generating a list of NavigationButtons and try to adjust their style now.
While using .v-touchkit-navbutton .v-touchkit-navbutton-desc in my one style that part works pretty well for me, but styling the caption seems to be more difficult than I thought...

I already added main styles successfully to .v-touchkit-navbutton as eg. background, border etc.
But now I can't figure out how (if possible at all) I can set any padding or font styles for the caption. I only was able to give a color to it, nothing more.

Does anyone have a hint for me how to do that or where to search?

Thanks in advance!

Best Regards
Manfred