Windows 11 new Contrast Theme affects many apps including Eclipse, Before open Eclipse app, just turn off your Windows 11 Contrast Theme by Press left Alt + Left Shift + Print Screen to turn off your Windows's Contrast Theme, and then open your Eclipse app, all the Eclipse's own themes can now be used as you wish. Now tab out to go back to Windows, Press left Alt + Left Shift + Print Screen to turn on Windows 11 new Contrast Theme, now back to Eclipse, the system ask you to re-start the app to enable Contrast them, you click no and enjoy programming with Eclipse's theme (dark theme).