CSS frameworks are predefined styling libraries written into Cascading Style Sheet language with W3C standard compliant. These CSS frameworks are useful to save your time and efforts to design a website or its parts. These are ready to serve bunch of codes which can be used without or with little changes with your website styling. Another advantage about these CSS frameworks is learning resources. These are the best learning resources for CSS styling, more the time you spend with these frameworks more you will learn about CSS styling.
W3C regulates all major versions of CSS styling, and your website should be according to those rules set by W3C for better search engine listing and SEO boost. Your website design depends upon CSS and you will make it furnish with the help your these CSS frameworks.
Go further and get the 15 best CSS frameworks to the date, these will surly boost your web development process and you will get more time to do other work.