Using "go build", compile executable files for three platforms.
The executables have only been tested on Windows 10 and Linux 8.
Improved the program to handle the "unsupported pseudo-class selector" error.
#1 (comment)
The original program was using the css selector package ericchiang/css. Clearly, this package didn't offer robust support for pseudo-class selectors. Now, I've switched to another package, andybalholm/cascadia, which provides the necessary support.