In this tab you can specify Google Web Typefaces to be used in various parts of the theme.For each elements listed below you can choose any front from the Google Web Font library. Once you have chosen a font from the list, you will see a preview of this font immediately beneath the list box. Icons will appear on the right hand side of the preview. These icons indicate what font weights are available for that chosen typeface. The Icons are as follows:
R -- Regular
B -- Bold
I -- Italics
BI -- Bold Italics
When deciding what font to use, ensure that the chosen font contains the font weight required by the element in the theme, where it is being applied. For example, All main headings are bold, so you need to select a new font for these elements which supports a bold font weight. If you select a font which does not have a bold icon, the font will not be applied.
The full list of available fonts and their respective weights can be seen in the Google Web Font Library