The problem

Currently we have media queries, but in most cases widgets have not the full width of the viewport.

Partial solutions

Flexbox and grid layouts support some kind of inner responsiveness.

ResizeObserver to the rescue

For more complex scenarios we have to use JavaScript currently. There are a lot of container query libraries, most of them overcomplicated to my taste. (One of the reasons why it is not yet in CSS.)


Update - container queries have been arrived meanwhile!