Add Custom Body Class (See related posts)

// Add my-custom-class to body tag

function custom_body_class($classes) {
	$classes[] = 'my-custom-class';
	return $classes;
}
add_filter('thesis_body_classes', 'custom_body_class');

// To single pages only

function custom_body_class($classes) {
 if (is_single()) {
	$classes[] = 'my-custom-class';
	return $classes;
 }
}
add_filter('thesis_body_classes', 'custom_body_class');