So many amazing things coming to CSS these days, but I have a feeling anchor positioning is going to be one that gains traction pretty quickly because it solves such a big pain point and is pretty easy to use.
Explored it in this video: https://youtu.be/DNXEORSk4GUit
Browser support is far from perfect atm, but as I show in the video the polyfill is great. https://github.com/oddbird/css-anchor-positioning