Issue #1490402 followup by sun: Redesign tabs and the content header.

core/modules/system/css/system.theme.css

@@ -443,12 +443,15 @@ ul.links a.active {
 /**
  * Markup generated by theme_menu_local_tasks().
  */
-.tabs {
+div.tabs {
+  margin: 1em 0;
+}
+ul.tabs {
   list-style: none;
   margin: 0 0 0.5em;
   padding: 0;
 }
-.tabs__tab {
+.tabs > li {
   display: inline-block;
   margin-right: 0.3em; /* LTR */
 }