Are you asking about the IMGUI paradigm or DearIMGUI the library? In the case of DearIMGUI: - it does not handle theming (but forks do) - I don't know what reflow is - in a way, GPU acceleration is the default. In fact, DearIMGUI doesn't handle anything at all in that regards because it doesn't have to. You are the one responsible for drawing, DearIMGUI just outputs you a vertex buffer that you send to the GPU the way you want to. There are proposed backends but you can totally roll your own. People even have made networked and web backends. I don't know how those work.