Description from extension meta
Custom CSS Tester Tool for YouTube Comment Viewing UI
Image from store
Description from store
This custom CSS tester allows you to load a custom CSS to a YouTube Live Chat Comment page so that CSS customized version of the page can be viewed on your Web browser.
The CSS loaded to the page can be debugged with browser's built-in developer tools.
Please start in the extension's option page to set-up and open a Live Chat comment URL. Once a comment page is opened, the popup page can be used to temporarily edit and hot-reload the custom CSS inserted by this extension.
Support Page: https://kii-memo.blogspot.com/p/cas-akaji-bot.html (In Japanese)