Index: src/wp-activate.php
===================================================================
--- src/wp-activate.php	(revision 27627)
+++ src/wp-activate.php	(working copy)
@@ -64,6 +64,21 @@
 }
 add_action( 'wp_head', 'wpmu_activate_stylesheet' );
 
+/**
+ * Adds a class to the body element for activation in multisite.
+ * 
+ * @since 3.9.0
+ *
+ * @param array $classes Current classes assigned to the body element.
+ * @return array Classes to assign to the body element.
+ */
+function wp_activate_body_class( $classes ) {
+	$classes[] = 'wp-activate';
+
+	return  $classes;
+}
+add_filter( 'body_class', 'wp_activate_body_class' );
+
 get_header();
 ?>
 
Index: src/wp-signup.php
===================================================================
--- src/wp-signup.php	(revision 27627)
+++ src/wp-signup.php	(working copy)
@@ -41,6 +41,21 @@
 $wp_query->is_404 = false;
 
 /**
+ * Adds a class to the body element for signup in multisite.
+ *
+ * @since 3.9.0
+ *
+ * @param array $classes Current classes assigned to the body element.
+ * @return array Classes to assign to the body element.
+ */
+function wp_signup_body_class( $classes ) {
+	$classes[] = 'wp-signup';
+
+	return  $classes;
+}
+add_filter( 'body_class', 'wp_signup_body_class' );
+
+/**
  * Prints styles for front-end Multisite signup pages
  *
  * @since MU