You are correct. If you control the webpage, just get good and write correct CSS (including new CSS layers). If you don’t control the page, Shadow DOM is actual

You are correct. If you control the webpage, just get good and write correct CSS (including new CSS layers). If you don’t control the page, Shadow DOM is actually leaky in weird ways (inheriting fonts and colors, for example), so you want an iframe. There’s not many good uses for it, and it should be a CSS thing, not a JS thing anyway.