And as for detecting updates to the CSS file and refreshing the web preview automatically, that's a bit more complicated. I'm not sure if that should even be attempted.
In BBEdit this works! The Web Preview will be updated each time you save the CSS file which is 'used' by the HTML file in the Preview.
This one little (but major) thing that don't let me kill BBEdit from my Applications Folder! I would love to do that and sooo much!
-Nico