- using the cache level with value of “Standard”
At your hosts/origin you can setup cache-control headers and more. Moreover, even at Cloudflare dashboard this is possible.
You actually do not need any page rule for the assets under the folders:
In case you want you can try to add a Page rule should look like this for example:
Cache Level: Cache Everything
Cloudflare will cache by default static files, you can check all file types that are cached here: