How to change the font for a Chart Legend

I have a line chart, displaying 3 series. Beautiful thing to see. GXT is wonderful!

But the title, axis labels, etc, are all in Arial, and the series legend is in Times Roman.

I cannot see where the font is changed. Not on the Chart object. Not on the Series. Not in the Legend configuration. Is there a Sprite object somewhere I can configure to alter this?

Any thoughts?