Change Day and Date Column Header Font

How can I change the font for the column headers (day and date).

I have added the attrribute - CssClassPrefix="scheduler_" and I have added the following styles to the css.

.scheduler_timeheadergroup
{
font-family: Verdana;
font-size: 7pt;
}

.scheduler_timeheadercol
{
font-family: Verdana;
font-size: 7pt;
}

However the font still does not change. I have tried setting all of the other attribute to nothing HeaderFontSize="" etc...

This is the Scheduler / Resource view.