This is a draft CSS parser written in C++ using the PEGTL 2.x library (because a dependent project does not want to move to C++17 that PEGTL 3.x requires).
Once you configure and build the project, run
./parse-css file.cssand you will see a stream of all the grammar matching done. It is not pretty, but it allows hand-validation and debugging.
Turn off DBG_PARSE in parse-css.cxx and it will not
print these matches as it goes.
Instead, it will print a summary at the end and information
about how many rulesets and properties it encountered (which
is not perfectly computed at this point).
Turn off DBG_GRAMMAR in parse-css.cxx and it will not
invoke PEGTL's grammar analysis (cycle detection) before
parsing.