The style properties like
Code:
    GtkButton::default_border         = {0, 0, 0, 0}
    GtkButton::default_outside_border = {0, 0, 0, 0}
    GtkButton::default_spacing        = 10
aren't engine specific, all of them are gtk properties so they apply to any engine.

About the murrine engine
http://cimi.netsons.org/pages/murrine/options.php