Twitter's mobile app for Android and iOS has a night mode which has a dark theme. It is not available for the twitter web app yet. This extension brings the night mode to web. Night mode is enabled by default and it can be switched to the default theme by clicking on the twitter icon that shows up in the tool bar when you visit twitter.com. From version 0.0.4, this extension applies the night mode to theme to all twitter pages.
If you see some dark text that are hardly visible on dark mode, you might have to change your twitter theme from "Edit Profile" page.
This extension *does not* access your personal data.
I wrote about it here - http://tsriram.in/2016/08/24/bringing-twitter-night-mode-to-web/
Please feel free to report issues and share feedback here - https://github.com/tsriram/twitter-web-night-mode/issues