Eclipse became famous not only for being a first quality Java IDE developed with extensibility in mind, but also because it has a light graphic interface that is equal to the interface of the operational system where it's being executed. This graphic interface was separated from IDE main code and became what we know today as SWT (Standard Widget Toolkit).

SWT is a component layer over operational system standard components. A SWT button is in fact a button of your operational system. So if you apply a theme that changes the color or shape of your button, SWT button will modify in conformity with your new theme.

SWT Java applications always have the look of the operational system where they are executed in because they directly use those components to generate screen visualization. This approach lets the applications to interact with the environment in a better way, making them appear to be more natural to users and even lighter.