This is a customed Visual Studio 2013 theme for AvalonDock. Simply modified it to work with AvalonDock v2.9.
The origin repo is https://github.com/4ux-nbIx/AvalonDock.Themes.VS2013/tree/master/Xceed.Wpf.AvalonDock.Themes.VS2013, but I cannot use the origin one and did some customization.
<xcad:DockingManager.Theme>
<vs2013:Vs2013DarkTheme />
</xcad:DockingManager.Theme>
To install AvalonDock.Themes.VS2013, run the following command in the Package Manager Console
Install-Package AvalonDock.Themes.VS2013