Add custom classes and ids plus first, last, even, odd, and numbered classes to your widgets.
You need to make sure you have an HTML element defined for
after_widget in your active theme's
usually located in your theme's functions.php (/wp-content/themes/yourtheme/functions.php).
This HTML element must have class and id attributes. This plugin will not work if
after_widget are blank.
register_sidebar( array( 'name' => 'Sidebar', 'before_widget' => '<div id="%1$s" class="widget %2$s">', 'after_widget' => '</div>', 'before_title' => '<h2 class="widget-title">', 'after_title' => '</h2>' ) );
There are two ways:
Edit your theme's style.css file (usually located in /wp-content/themes/yourtheme/).
Use a plugin such as Simple Custom CSS.
You can export the Settings from Settings > Widget CSS Classes > Import/Export.