You don’t need to worry much about the recommendation on the code. It is not error as such.
It 's just saying You have -webkit added (mostly for Chrome) and for backward compatibly may wish to add -o-transition and -moz-transition too (for older Opera and Mozilla -Firefox- browsers. I’m not really sure is -webkit is needed now.
I am not sure why it is not working, but did remove the dot when adding the “hover-zoom-in” class to the module?
If you can post a link it would not take long to see what is happening. The other thing is caching.