Of course, but to change the extensions of each html document is not desirable to me
because I try to have static resources wherever possible ( EP limits )
and it’s easier to run/test because I don’t need to turn on the local web server.
It’s still easy when someone has one CSS file, but I often see that many have more than 10 
If you frequently make changes to CSS and other resources
you can also play with the Cache-Control settings and reduce the values from various parameters (how many seconds will hold something in the cache) or ETag…