Serving static files from google cloud storage?

I'm not sure how you are uploading your files and why the public read is not set correctly, but you could also change that through the Google Cloud Storage Manager. Simply locate the bucket and the file and click on the Share Publicly checkmark and you'll get the link.

Or you can upload that file using the gsutil with public read right away:

gsutil cp -a public-read custom.css gs://my_backet