Index: wp-content/themes/twentyfifteen/header.php
===================================================================
--- wp-content/themes/twentyfifteen/header.php	(revision 29994)
+++ wp-content/themes/twentyfifteen/header.php	(working copy)
@@ -30,7 +30,7 @@
 		<header id="masthead" class="site-header" role="banner">
 			<div class="site-branding">
 				<h1 class="site-title"><a href="<?php echo esc_url( home_url( '/' ) ); ?>" rel="home"><?php bloginfo( 'name' ); ?></a></h1>
-				<h2 class="site-description"><?php bloginfo( 'description' ); ?></h2>
+				<p class="site-description"><?php bloginfo( 'description' ); ?></p>
 				<button class="secondary-toggle"><?php esc_html_e( 'Menu and widgets', 'twentyfifteen' ); ?></button>
 			</div><!-- .site-branding -->
 		</header><!-- .site-header -->
Index: wp-content/themes/twentyfifteen/style.css
===================================================================
--- wp-content/themes/twentyfifteen/style.css	(revision 29994)
+++ wp-content/themes/twentyfifteen/style.css	(working copy)
@@ -1304,7 +1304,7 @@
 	font-size: 1.2rem;
 	font-weight: 400;
 	line-height: 1.5;
-	margin-top: 0.5em;
+	margin: 0.5em 0 0;
 	opacity: 0.7;
 }