Popup during backend process

Hi,

I want to show the processing icon in a popup by graying out the background during a backend save operation on click of a button.

Could you please suggest which component is best for this? And how can I grey out the main panel and show the popup on top.

The popup should be able to be closed once the save operation is completed which can be done in the callback method.

Please help!

Thanks
Thiruppathy.R