Widget Variations allow for the individual styling of each widget within a position, without it being global. Code wise, this is achieved by selecting a variation in the each widget settings panel, which will add a class to that widget. The theme CSS adjusts accordingly.
Choose any available options at Appearance → Widgets → Your Widget → Widget Style
There are 3 standard suffixes: titlecolor, simple & background. All widgets can apply the titlecolor suffix, and simple & background only apply to the gantry widgets and positions : maintop, content-top, content-bottom and sidebar positions.
However, there is also a non-standard suffix showcase, which applies to the showcase-a/f positions. This affects the module title as seen on the frontpage, i.e. Popular