TwentyFifteen|Sixteen themes have a `<div id="content">` in the header. Change the `<div>` IDs in `wp-activate.php` and `wp-signup.php` to be unique to each page.

Props jfarthing84.
Fixes #33843.


git-svn-id: https://develop.svn.wordpress.org/trunk@34162 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-activate.php

@@ -67,7 +67,7 @@ add_action( 'wp_head', 'wpmu_activate_stylesheet' );
 get_header();
 ?>
 
-<div id="content" class="widecolumn">
+<div id="signup-content" class="widecolumn">
 	<?php if ( empty($_GET['key']) && empty($_POST['key']) ) { ?>
 
 		<h2><?php _e('Activation Key Required') ?></h2>

src/wp-signup.php

@@ -75,7 +75,7 @@ get_header();
  */
 do_action( 'before_signup_form' );
 ?>
-<div id="content" class="widecolumn">
+<div id="signup-content" class="widecolumn">
 <div class="mu_register">
 <?php
 /**