Removed margin from row element

IPython/html/static/tree/less/tree.less

@@ -127,6 +127,11 b' input.engine_num_input {'
    
 }
 
+.tab-content .row {
+    margin-left: 0px;
+    margin-right: 0px;
+}
+
 .folder_icon:before {
     .icon(@folder-close-alt)
 }