Custom CSS Hover - Saving Issue

Hi all,

I'm having an issue with saving a custom css hover to my image files for one of my pages.

I'll add the custom code for hover for my images and it'll work perfectly while viewing it on the custom page. However, when I try to hit the "Save" button, at the top left corner of the SS screen, my hover style fails and does not work. Is this a SS bug or an issue that I've caused?

Thank you for your help!