If you can block modal dialog with z-index?

Good day!

I make the preloader wait for completion handler of the button click. The button is in a modal window.
Page created translucent div block that when clicked should cover the entire page and not allow to do anything, and at the end of the event handler, to return to the zero layer.

To implement this I thought changing the z-index. But the problem is that when setting the class loading for the block preloader - modal form remains on top and active. Tell me how can I implement a preloader or how else can you lock the form?

.loading {position: fixed;display: block;top: 0;left: 0;width: 100%;height: 100%;z-index: 1000;background-color:black;opacity:0.3;}