Please try out this CSS and see if it fits. It is not exactly the effect because you can not cut the edges on that background on hover, as it would normally be with the zoom effect of the Image Frame Widget. Nonetheless it should do the trick.
#mobile-menu .mega-menu .sub-menu li a::before,
#main-nav .mega-menu .sub-menu li a::before {
transition: all 0.3;
}
#mobile-menu .mega-menu .sub-menu li a:hover::before,
#main-nav .mega-menu .sub-menu li a:hover::before {
-webkit-transform: scale3d(1.1, 1.1, 1);
-ms-transform: scale3d(1.1, 1.1, 1);
transform: scale3d(1.1, 1.1, 1);
}