Styling Sidebar

how to call each widget and assign them different classes

how did you use ‘register_sidebar()’ in functions.php of your theme?

the parameters in ‘before_widget’ – 'before_widget' => '<li id="%1$s" class="widget %2$s">' would add individual css classes and ids to each widget.

http://codex.ww.wp.xz.cn/Function_Reference/register_sidebar

there is a related topic for even more css classes:
http://ww.wp.xz.cn/support/topic/how-to-first-and-last-css-classes-for-sidebar-widgets?replies=9