fixes #8900: nuke empty space between panel heading and list group

dist/css/bootstrap.css

@@ -2426,6 +2426,14 @@ a.list-group-item.active .list-group-item-text {
   border-bottom: 0;
 }
 
+.panel-heading + .list-group {
+  margin-top: -15px;
+}
+
+.panel-heading + .list-group .list-group-item:first-child {
+  border-top-width: 0;
+}
+
 .panel-heading {
   padding: 10px 15px;
   margin: -15px -15px 15px;

less/panels.less

@@ -11,8 +11,14 @@
   border: 1px solid @panel-border;
   border-radius: @panel-border-radius;
   .box-shadow(0 1px 1px rgba(0,0,0,.05));
+}
+
+// List groups in panels
+//
+// By default, space out list group content from panel headings to account for
+// any kind of custom content between the two.
 
-  // List groups in panels
+.panel {
   .list-group {
     margin: 15px -15px -15px;
 
@@ -30,6 +36,13 @@
     }
   }
 }
+// Collapse space between when there's no additional content.
+.panel-heading + .list-group {
+  margin-top: -15px;
+  .list-group-item:first-child {
+    border-top-width: 0;
+  }
+}
 
 // Optional heading
 .panel-heading {