Here is a simple filter to automatically add a class attribute like widget-order-1 to all widgets within sidebars:

My colleague Kaspars Dambis published a blog post recently outlining a cunning way to “add a class attribute like widget-order-1 to all widgets within” widget areas in WordPress. This works very well and allows you to target specific widgets with different styling (eg: the first, second, third widgets etc). This is an extremely handy feature when you are attempting to style widget areas within WordPress.

I’ve added an extra feature to Kaspars code, by adding support for “.first-widget” and “.last-widget” classes, so that you know which widget is at the very start and ends of your widget areas. This can be useful for situations in which the last widget needs to look slightly different from the rest, eg: if it should not have a separator line below it.

If you can see any ways to improve this code, please let me know!

/**
* Adds order class to widgets
* Useful for targetting individual widgets
*
* Works by modifying the global array containing the sidebar class names
* Code adapted from http://konstruktors.com/blog/wordpress/3615-add-widget-order-css-class-sidebar/
*
* @since 1.0
* @global array $wp_registered_sidebars
* @global array $wp_registered_widgets
* @author Ryan Hellyer <ryan@pixopoint.com> and Kaspars Dambis <kaspars@metronet.no> and
*/
function slug_widget_order_class() {
global $wp_registered_sidebars, $wp_registered_widgets;
// Grab the widgets
$sidebars = wp_get_sidebars_widgets();
if ( empty( $sidebars ) )
return;
// Loop through each widget and change the class names
foreach ( $sidebars as $sidebar_id => $widgets ) {
if ( empty( $widgets ) )
continue;
$number_of_widgets = count( $widgets );
foreach ( $widgets as $i => $widget_id ) {
$wp_registered_widgets[$widget_id]['classname'] .= ' widget-order-' . $i;
// Add first widget class
if ( 0 == $i ) {
$wp_registered_widgets[$widget_id]['classname'] .= ' first-widget';
}
// Add last widget class
if ( $number_of_widgets == ( $i + 1 ) ) {
$wp_registered_widgets[$widget_id]['classname'] .= ' last-widget';
}
}
}
}
add_action( 'init', 'slug_widget_order_class' );