This is a recreation of the Fork me on GitHub ribbon in CSS, hence resolution-independent.
CDN provided by cdnjs
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/github-fork-ribbon-css/0.1.1/gh-fork-ribbon.min.css" />
<!--[if lt IE 9]>
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/github-fork-ribbon-css/0.1.1/gh-fork-ribbon.ie.min.css" />
<![endif]-->See 'em in action! https://simonwhitaker.github.io/github-fork-ribbon-css/
Feel free to fork, tweak and send me a pull request.
Note: this project is not sponsored or in any way endorsed by GitHub.