This solution consists of a PostCSS plugin and a JS (Container) class that
takes care of runtime styling.
PostCSS → Metadata → Runtime
The plugin analyses your CSS and extracts all container query related data, producing a metadata object.
Depending on your setup this file could contain more than one container's data. (See Multiple Containers for more details.)
Once you have your metadata, all you need to do is to feed it to the Container instance, and it will take care of the rest!
Your job is even easier in React, as Container instantiation is abstracted away.
One important note on containers:
For container queries and units to work, all elements using container queries must be descendants of a container, as their conditions and values only makes sense in a container's context.)