Currently CSS syntax validator is using its own rules to validate CSS. These rules are outdated and confuses users (csstree/csstree#171). So the rules should be fixed or replaced with csstree's validator.
An alternative option to reject the validator's page and redirect to CSS syntax reference where will be a functionality to validate CSS syntax. This option looks more promising to me, because in addition to CSS validating according to existing syntax definitions, I would also like to add the ability to supplement or redefine syntax definitions.
Currently CSS syntax validator is using its own rules to validate CSS. These rules are outdated and confuses users (csstree/csstree#171). So the rules should be fixed or replaced with csstree's validator.
An alternative option to reject the validator's page and redirect to CSS syntax reference where will be a functionality to validate CSS syntax. This option looks more promising to me, because in addition to CSS validating according to existing syntax definitions, I would also like to add the ability to supplement or redefine syntax definitions.