I solved this myself a while back using the Global Dark style available at userstyles.org: https://userstyles.org/styles/31267/global-dark-style-changes-everything-to-dark. You can view the CSS from here, and you may not need all the code so you can significantly cut down on it. Here's how to inject .css from a file:
Tanay Neotia 11 months
So I am using Flutter's webview_flutter plugin that does not support dark mode. What I would like to do is have a CSS or JS script that I can inject into any page that I load so that basically all the things that are white turn black/dark (like backgrounds) and all the things that are dark/black turn white (like text). I want to leave the non black/white colors of the website exactly the same. How can I go about doing this?