The Microsoft Edge web browser included with Windows 10 also has a dark theme.
A few desktop applications, including File Explorer and Paint.NET, do respect this setting-but most don’t. And, as we mentioned before, this option doesn’t affect most desktop applications. However, it’s up to each developer to support Dark Mode, and many do not. The Settings application itself immediately turns dark, as will many other “Universal Windows Platform” applications (those you get from the Windows Store). Scroll down and select the “Dark” option under the “Choose your app mode” section. To enable Dark Mode, head to Settings > Personalization > Colors. Enable Dark Mode for Windows 10 Settings and Apps