> This popup implementation is no different than what is already possible with css There are certainly differences. Accessibility, tab functionality, semantics

> This popup implementation is no different than what is already possible with css There are certainly differences. Accessibility, tab functionality, semantics. But most importantly, browsers can sensibly position these to flow away from the edge of the screen when the containing element is at the edge of the viewport (previously with CSS you'd have to choose a direction, and would need Javascript to position anything based on the element's place in the viewport)