Add flexible column classes to widget areas.

genesis-flexible-widgets.php

<?php
/**
 * Add flexible widget classes.
 *
 * @param  string $id Widget area ID.
 * @return string $class Flexible widgets CSS class.
 */
function starter_widgets_flex_class( $id ) {

	global $sidebars_widgets;

	if ( isset( $sidebars_widgets[ $id ] ) ) {
		$count = count( $sidebars_widgets[ $id ] );
	}

	$class = '';

	if ( 1 === $count % 5 ) {
		$class = ' flexible-widgets-5';
	} elseif ( 1 === $count % 4 ) {
		$class = ' flexible-widgets-4';
	} elseif ( 1 === $count % 3 ) {
		$class = ' flexible-widgets-3';
	} elseif ( 1 === $count % 2 ) {
		$class = ' flexible-widgets-2';
	} else {
		$class = '';
	}

	return $class;

}