First sorry for those errors on the CSS validator.
Please note that the “Warnings” we need to maintain due to cross-browser compatibility. For now to fix the “Errors” please replace all code of the files to:
* We only removed the errors on this file. The CSS that was generating the errors is not necessary anymore. This is a residual unremoved CSS between the Porto updates.
Doing this you will have the CSS files validating trough the validator tool.
Please, try that and let us know if you need further assistance.