I set a new z-index style because the original z-index in the ' style/zindex.css' is 65536, its so high and made me to avoid modify it directly to prevent possible overlaying by other components. Beside that, I've found these comments in the style/zindex.css:

>     /* zIndex of important system app parts
>      * is gathered here to clearly specify all system-app hierarchy */

I think the original intention here  is to manage all z-index settings in a place to prevent them scatter about the whole app. But if modify the original one or set a literal value in the code is OK, I will fix it.