Two years ago I asked [Wayback/Archive] Jeroen Wiert Pluimers on Twitter: “Is there a way to make the @github gist text editor wider and taller? Right now (at 1920×1200) it uses about half the screen width and screen height. That wastes about 25% of screen estate. “.
I still have to figure out how to fix the height, but the width was relatively easy back then. Hopefully this CSS fix still works today.
In the mean time [Wayback/Archive] Add full height gist creation by xthexder · Pull Request #68 · xthexder/wide-github: Conversation permanently fixed my problem.
[Wayback/Archive] Jeroen Wiert Pluimers on Twitter: “I fixed the width by modifying .container-lg and changing max-width from 1018px to 95%.”
Until GitHub fixes it themselves, I started with this fix in the extension [Wayback/Archive] Stylus – Chrome Web Store:
The Wiert Corner - irregular stream of stuff 