The Github copy of Storefront requires you to run grunt to compile the stylesheets etc and you can read more about that below in the section Set up your development environment.
Contributor Guidelines: https://github.com/woothemes/storefront/blob/master/CONTRIBUTING.md
You can also download the theme from here https://wordpress.org/themes/storefront/ as it’s already compiled.
Can you check it have style.css file inside it? go inside and see if it exists or not?
if not you have to download it again. if it exists, Then give me link of theme.. and let me check for you
If you’re going to download from github and aren’t a developer, always download from the releases page – https://github.com/woothemes/storefront/releases
