Responsive graphical user interfaces, which can adapt to changes in display size, improve the user experience and are easier to developand maintain compared to ones relying on absolute (pixel) placement. Based on a survey of several responsive frameworks across desktop, mobile and web platforms, we design and develop a backwards- compatible responsive extension of an existing non-responsive Lua GUI framework. We also provide the specification that describes the features selected to be part of the new responsive framework, as well as some implementation details pertaining to those features.