As part of the GSoC 2024 project "Improvements to the Blender macOS User Interface Experience" [1], this patch implements colored titlebar window decorations on macOS, based on the current Blender theme colors. Additionally, this patch introduces a new WM/GHOST API for implementing and enabling custom decoration styles on any system/desktop environment that support customizing window decorations. [1]: https://devtalk.blender.org/t/gsoc-2024-proposal-improvements-to-the-blender-macos-user-interface-experience/34022) Pull Request: https://projects.blender.org/blender/blender/pulls/123982