When using the Neptune theme under Ext 188.8.131.523, a small gap appears (through which the document's white background color can be seen) below a tabpanel's tabBar, as shown in the attached "normal-neptune.png" file.
This can be fixed, as shown in the attached "patched-neptune.png" file, by adding the "x-tab-default-active" CSS class' definition to the "x-panel-default" CSS class, as follows.
Please correct this issue in ExtJS itself so that I can stop using the above patch. Thanks!
/* fill up the background gap directly below a tabBar */
background-color: #add2ed; /* .x-tab-default-active */