PrimeNG has been providing Grid CSS layout utility to serve as the official grid system however it has limitations because of the float based design. In order to modernize it, we’ve introduced a new Grid System called PrimeFlex which is a lightweight flex based responsive layout utility optimized for mobile phones, tablets and desktops. Flex Grid CSS is not included in PrimeNG as it is provided by PrimeFlex, a shared grid library between PrimeFaces, PrimeNG and PrimeReact projects.
Grid CSS on the other hand is deprecated now, it will not be included in primeng.css in PrimeNG 8 however there are no plans to remove it, if you like to keep using it for backward compatibility, you may include it manually since it will be shipped with PrimeNG distribution.
See the FlexGrid demo at PrimeNG Showcase that utilizes PrimeFlex.
PrimeFlex is available at npm for download. Once it is downloaded to your node_modules, you may use css imports or angular-cli.json to add it to your project.