I'm not entirely sure what you're asking but I assume this is what you're looking for as the the two features that can be achieved using CSS postprocessors are:
1. Error checking: CSS preprocessors can help detect syntax errors, misplaced brackets, and other common mistakes made while writing CSS code. This can save time and effort in debugging and fixing errors in the code.
2. Fallbacks for newer CSS features: CSS preprocessors can help provide fallbacks for newer CSS features that may not be supported by all browsers. For example, if a certain CSS property is not supported by a particular browser, a preprocessor can automatically generate a fallback for that property, ensuring that the website or application looks and functions as intended.