jQuery Mobile Docs - Button icons: "Adding Icons to Buttons
The jQuery Mobile framework includes a selected set of icons most often needed for mobile apps. To minimize download size, jQuery Mobile includes a single white icon sprite, and automatically adds a semi-transparent black circle behind the icon to ensure that it has good contrast on any background color.
An icon can be added to a button by adding a data-icon attribute on the anchor specifying the icon to display. For example, the following markup:"
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