Unity only uses native UI systems for Window management, input handling, and menus/file dialogs. The rest of Unity's UI is intentionally written in Unity's own

Unity only uses native UI systems for Window management, input handling, and menus/file dialogs. The rest of Unity's UI is intentionally written in Unity's own GUI. We chose GTK over QT for Linux because Unity 5.1 ships with CEF (https://en.wikipedia.org/wiki/Chromium_Embedded_Framework https://en.wikipedia.org/wiki/Chromium_Embedded_Framework) as the embedded browser and CEF already pulls in a dependency on GTK).