"OK" & "Cancel" button not working in full screen mode for image cropper dialogue (7.8)

Reproduction steps:--
1.Login to Cms
2.Select any image and edit it.
3.click on "crop image" link on Thumbnail (large).
4.Click on Full screen button.
5.Click on Ok button shown in the bottom right corner.
6.A blank popup opens.
7.Same is applicable for cancel button.

Actual result:-->'OK' & "Cancel" button should work properly in full screen mode.
Expected result:->"OK" & "Cancel" button not working in full screen mode for image cropper dialogue.