Try to use file2hd.com or (google search 'file2hd Unblocked') That works for most websites unless the creator has set up specific headers or security measures to prevent such access. I use it alot for learning other peoples code. if this fails use firefox developer edition click on the menu icon then 'save page as' > complete website, within the folder that has been saved you should be able to view or locate the css file. Another alternative would be to use the developer tools click on the body, navigate to computed styles and just copy them manually (Although this would probably be a long and tedious task). Hope one of these helps.
Another Alternative to File2hd that you could try is:
robin-goods: Website Dowloader
!Sorry That one only links to an article about it, heres the actual App: websitedownloader.io
You can also view this answer for more refference: Download css, js , images of website