aero.msstyles

Windows visual style

A .msstyles file contains a visual style, the theme appearance of Windows. The file is a PE binary that holds images, colors, and metrics for windows and controls. The known file is aero.msstyles in the Resources directory of Windows. The theme service loads the style that the current theme selects. Third-party styles need a patched system, which Microsoft does not support.

A file extension is only a part of the file name. It does not give a guarantee about the format or the content of a file. But on Windows, the extension selects the program that opens the file.