z-index problem

I have a grid control defined, with split mode and footer. Everithing works fine, but I need to use a DIV to display a grid as a modal dialog (not realy a modal dialog), but the context menu and all controls in the grid never display over the DIV. They display under it. I tried changing z-index in context.css but nothing happens. What can I do? Im using grid 1.5.

The z-index of controls in the grid can be defined in dhtlmxgrid.css

    .dhx_textarea{
    .dhx_combo_select{

The z-Index of menu can be specified during menu initialization

    var cmenu=dhtmlXContextMenuObject(…
    cmenu.menu.setZIndex(NN);