Chang background in JS stop working after update C3

For some reason in my project after I updated to 379 the JS background color changing "document.body.style.backgroundColor =" as well as putting image on a background by "document.body.style.backgroundImage = "url('img.png')"" doesn't work now :(

could you share an example? I would try to check it in the browser to see if the url is available and the path is ok.