LMS: revises membership UI layout on instructor dashboard

lms/static/sass/course/instructor/_instructor_2.scss

@@ -329,16 +329,12 @@ section.instructor-dashboard-content-2 {
 .instructor-dashboard-wrapper-2 section.idash-section#membership {
   $half_width: $baseline * 20;
 
-  .vert-left,
-  .vert-right {
-    display: inline-block;
-    vertical-align: top;
-    width: 48%;
-    margin-right: 2%;
-  }
+  .membership-section {
+    margin-bottom: $baseline;
 
-  .vert-right {
-    margin-right: 0;
+    &:last-child {
+      margin-bottom: 0; // last child!
+    }
   }
 
   .batch-enrollment, .batch-beta-testers {

lms/templates/instructor/instructor_dashboard_2/membership.html

@@ -26,7 +26,7 @@
   </div>
 </script>
 
-<div class="batch-enrollment">
+<section class="batch-enrollment membership-section">
   <h2> ${_("Batch Enrollment")} </h2>
   <p>
     <label for="student-ids">
@@ -66,10 +66,10 @@
   </div>
   <div class="request-response"></div>
   <div class="request-response-error"></div>
-</div>
+</section>
 
 %if section_data['access']['instructor']:
-<div class="batch-beta-testers">
+<section class="batch-beta-testers membership-section">
   <h2> ${_("Batch Beta Tester Addition")} </h2>
   <p>
     <label for="student-ids-for-beta">
@@ -109,10 +109,10 @@
 
   <div class="request-response"></div>
   <div class="request-response-error"></div>
-</div>
+</section>
 %endif
 
-<div class="member-lists-management">
+<section class="member-lists-management membership-section">
   ## Translators: an "Administration List" is a list, such as Course Staff, that users can be added to.
   <h2> ${_("Administration List Management")} </h2>
 
@@ -213,7 +213,7 @@
     ></div>
   %endif
 
-</div>
+</section>
 
 %if course.is_cohorted:
 <hr class="divider" />