An open-source project started by Nicholas C. Zakas and Nicole Sullivan. One of the most well-known CSS tools.
CSSLint is most often used for maintaining consitency with a house style guide but it can also be an easy way to integrate syntax checking into a build pipeline.
To integrate this into a build pipeline, your best option is probably the most well-known CSS testing tool: CSSLint as, aside from everything else it offers, it provides syntax checks. Importantly, it has great community support so there are already plugins for the most common continuous integration setups.