I was sad to see that its been 8yrs and only Firefox supports css element().
Fortunately with the help of some clever scss and css variables. I have been able to implement a polyfill. There are some limitations and I would not call it performant but its not the worst I have ever seen.
I will see if I can get a better version working with the Paint Api.
You might be thinking, this is useless?
well compositing live blur effects would be fairly simple using this approach, something I have sort of done before in other pens but not as elegantly as this.