It would be really nice if you init variable bodyStyle with = document.body.style somewhere earlier in widjet.js lifecycle before using it as undefined in updateWidgetStyle() to document.body. For example createWidget() seems to be nice place for initialization.
Thank you.

P.S. same issue https://forums.rocket.chat/t/livechat-script-omnichannel-removes-style-attribute-from-body/9940