Changing style-elements in a css-file that is imported by a main-css-file(index.css for example) with the @import-derective doesn't work. Changes in those css-files are completely ignored. The only solution is to import all the css-files with the <link rel="stylesheet"> tag in the index.html file.
A bug or settings that have to be adjusted?
You are seeing this issue because @import causes the specified css file to be downloaded when the parent css file is being loaded. Any changes that you make will not show up unless you reload the page since this page is not being constantly watched for changes.