modify style of gated page to match design

lms/templates/_gated_content.html

@@ -5,19 +5,22 @@ from django.utils.translation import ugettext as _
 from openedx.core.djangolib.markup import Text
 %>
 
-<div>
+<div class="xblock xblock-student_view xblock-student_view-vertical xblock-initialized">
     <h2 class="hd hd-2 unit-title">
         <span class="icon fa fa-lock" aria-hidden="true">&nbsp</span>${gated_section_name}
     </h2>
-    <h2>
+    <p/>
+    <h3 class="hd hd-3 problem-header">
         ${_("Content Locked")}
-    </h2>
+    </h3>
     <p>
         ${Text(_(
             "You must complete the section '{prereq_section_name}' with the required score before you are able to view this content."
         )).format(prereq_section_name=prereq_section_name)}
         <p>
-            <button><a href="${prereq_url}">${_("Go to Prerequiste Section")}</a></button>
+            <a href="${prereq_url}" class="btn btn-brand">${_("Go to Prerequiste Section")}
+                <span class="sr">${_("Go to Prerequiste Section")}</span>
+            </a>
         </p>
     </p>
 </div>