CSS (:not) is causing errors on build

[Nic-84]

Description of bug/issue:

I am using :has and :not identifiers in my CSS code, like this:

.header .nav-wrapper .nav ul li:has(a:not(.anchor-nav)) {display: block;}

This code is working great (in web browsers that support it) so as far as I know it's formed properly. However, when running it through the BuildBundlerMinifier, it's erroring out when it gets to this line, specifically when it gets to the colon before the ":not". Here are the errors I get: