The Close and Auto Hide buttons are not scaled in 4K screen with 200% DPI
It looks like the images are not scaled and they look very small when DPI scaling is set.
Here is how they look:

I've tried to play with the "enableHighDpi" patch, but it didn't help.
I'm using:
- 4K monitor (3840*2160)
- 200% DPI scaling
- DockPanelSuite.ThemeVS2005 (V 3.1.0) is used
- DockPanelSuite (V 3.1.0)
This is because the actual code to generate such images on the fly was not written with HDPI in mind.
You might modify the code to adapt to the needs and send back a pull request if you like.
Apparently the way this works is there is a bitmap somewhere in that gzipped resource somehow. In VS2012 theme, there is an ImageService with those https://github.com/dockpanelsuite/dockpanelsuite/blob/master/WinFormsUI/ThemeVS2012/ImageService.cs . Apparently the 2015 theme uses it too. There it uses ImageServiceHelper.GetImage, if there is some way to pass the scale to it, at least it could resize the bitmap. It would be nice if there was some way to edit the resources and add some variants of the images for bigger resolutions too.
I wish it was possible to reject different images at runtime. Because, if an application has SVG formatted images, and if it has ability to convert SVG to Image at runtime (using the current scale), DockPanelSuite should use these images instead of embedded ones.