This extension makes the initial background of a webpage black. Some darker themed websites will often flash white while navigating between pages, which can be harsh on the eyes. If there is interest in supporting this extension, I will try to develop it based on feedback from users.
As an initial proof of concept, there are no settings. The extension will make a web page's background black upon loading, then revert this change if it detects something else trying to change the background color as well. This will sometimes make it appear that the extension isn't working.