Hi lamp,
There is an extension that extends scss support and provides content assist for scss file.
Look for an extension called scss-scan, the full extension id is aaronphy.scss-scan.
After downloading the vsix file, please install the extension by going to Help -> CodeMix Extensions…-> Install from VSIX file… and select the vsix file to start the installation process.
Please let us know how it goes.
Cheers,
Sal