In general once Grid is available I’m not sure polyfilling it would be a great idea. I’d be more keen to initially use it as an enhancement (perhaps within @supports rules).

@Bryan given that Grid isn’t actually available live anywhere yet I chose not to so as not to clutter the code examples.

@Peter I’m not sure what about the opening statement is “breezily brushing away” this fact. I’ve been writing about Grid for 3 years or so, I don’t open every blog post with a long statement about support.