"Element Queries" is a third-party JS library, which allows you to have CSS events on elements (instead of the whole screen, as is the case for Media Queries). It introduces additional dependencies and performance overhead, but at the same time can make responsive behavior easier to design (especially if you cannot use flexbox and grid, yet). Personally, I would try to get started with Media Queries, and if that's not enough, add Element Queries.
The creator of Element Queries is an active member on Hashnode (YaY; Tommy Hodgins ) and I invited him to join this discussion :)