> CSS Injection is a vulnerability that occurs when an application allows untrusted CSS to be injected into a web page. This can be exploited to exfiltrate sensitive data, such as CSRF tokens or other secrets, by manipulating the page layout or triggering network requests based on element attributes.
Source: CSS Injection/README.md in PayloadsAllTheThings. From PayloadsAllTheThings by Swissky and contributors. MIT License, Copyright (c) 2019 Swissky.