I followed the Drupal Bootstrap sub-theming documentation: basically copied the CDN starterkit and renamed all the files and it seems to work. I then added a line to the empty css/style.css.
At first it didn't work except when I went to /admin/appearance/settings/ and clicked the advanced tab and set the theme to 'Bootstrap (Default)'.
I then made more modifications to the style.css, this time it didn't refresh on the pages. Checking the rendered pages I found the css file is coming as a mangled named css file.
What is involved in generated this mangled file and how to refresh after modifying css/style.css?
Can I choose a different theme from the Bootstrap settings page and still use my css modified styles?