remove background from accordion, and use border instead

docs/assets/css/bootstrap.css

@@ -3165,7 +3165,8 @@ a.thumbnail:hover {
   margin-bottom: 18px;
 }
 .accordion-group {
-  background-color: #f5f5f5;
+  margin-bottom: 2px;
+  border: 1px solid #e5e5e5;
   -webkit-border-radius: 4px;
   -moz-border-radius: 4px;
   border-radius: 4px;
@@ -3177,9 +3178,6 @@ a.thumbnail:hover {
   display: block;
   padding: 8px 15px;
 }
-.accordion-body {
-  margin-bottom: 2px;
-}
 .accordion-inner {
   padding: 9px 15px;
   border-top: 1px solid #e5e5e5;

less/accordion.less

@@ -9,7 +9,8 @@
 
 // Group == heading + body
 .accordion-group {
-  background-color: #f5f5f5;
+  margin-bottom: 2px;
+  border: 1px solid #e5e5e5;
   .border-radius(4px);
 }
 .accordion-heading {
@@ -19,9 +20,6 @@
   display: block;
   padding: 8px 15px;
 }
-.accordion-body {
-  margin-bottom: 2px;
-}
 
 // Inner needs the styles because you can't animate properly with any styles on the element
 .accordion-inner {