Certain complex GitHub Markdown documents don’t render well—or especially, print well—with the whitespace gutters on either side of the screen. This is especially true when there are complex tables in a document.

I use the following userContent.css stylesheet in my browser to override the use of gutters. This renders complex tables much better:

@-moz-document domain(github.com) {
 .container-lg { max-width: none !important; }
 .container-xl { max-width: none !important; }
}

Some tables are so complex that they still spill off the edge of the page even in portrait mode. To counteract this I adjust the print scaling, or print in landscape mode, or both.