StyleContext.addClass

Adds a style class to context, so posterior calls to gtk.style_context.StyleContext.get or any of the gtk_render_*() functions will make use of this new class for styling.

In the CSS file format, a #GtkEntry defining a “search” class, would be matched by:

entry.search { ... }

While any widget defining a “search” class would be matched by:

.search { ... }