How to use wordpress content class?

If I understood you correctly, this is what you are trying to achieve:

register_sidebar(array(
    'name' => 'Sidebar Name',
    'id' => 'sidebar-id',
    'before_widget' => '<div class="sidebar_area">',
    'before_title' => '<h4>',
    'after_title' => '</h4><div class="sidebar_content">',
    'after_widget' => '</div></div>',
));

References:

• register_sidebar