First of all this is not the 'big news' our president was referring to.
But it is still big news...

You, just like me and many others, have probably wasted valuable time looking at an XPP CSS file and wondering why it does not do what it was supposed to do. Only to find out, a couple of hours later, that you made a silly typo. Since CSS silently ignores all syntax errors, XPP will offer you no help.

So (out of frustration?) I have created a CSS syntax check tool that fully understands the XPP flavor of CSS. 
That is indeed big news, but it gets even better: this tool is available to you free of charge.
You can download it from github: https://github.com/Haf-Linger/XppCssCheck
That is also the place where you find the necessary documentation on how to install/run/integrate this tool.

You can run the tool from the command line. But it is a lot more efficient if you integrate it into Notepad++.

When you have a CSS file open in Notepad++, you simply hit the hotkey associated with the tool.
And you get something like:

Clicking on any of the error or warning messages will bring the cursor to the error/warning line in question, so you can easily correct your mistake.

This tool comes to you as open source software and is completely free (although donations are welcome!).
It is written in Perl and will only run on a system that has the XPP software installed on it.
A separate config file containing all the properties/values that XPP supports allows for easy updating the tool to any future properties/values that might get added to XPP.
(current config file contains all properties/values known to XPP V9.4 except for the paged media stuff)

As said before, Github is the place where you find the latest version and the documentation.
It is also the place where you can report any issues/questions/suggestions that you might have.
You might want to recheck from time to time for any updates that might have taken place. 

So don't be shy, give it a try...