ASP.NET NavigationMenu with dhtmlxGrid

Pls refer to attached image. The ASP.NET NavigationMenu is underneath dhtmlxGrid. I played with z-index of NavigationMenu but no use at all.

I also tried to change the z-index of the grid. The grid will not be shown if I set dhtmlxGrid to z-index=-1.

I ran into the same issue with dhtmlxForm. How should I tackle this issue?

Thanks in advance

I have found the solution. I need to add below style at page level:

<style type="text/css">
        z-index: 99999;

I don’t know why it does not work if I add it into the css file directly.

Attached is the image that shows correct display stack.