Newer versions of KSP support Unity’s updated UI system (technically available since KSP 1.0, but only really practical since 1.1), which is a major improvement over the old OnGUI system. Rather than rebuilding the UI every frame using the esoteric GUILayout and GUI system, the new Unity UI is built using standard Unity objects and hierarchies. This significantly improves performance, reduces the garbage created, and allows for some fancy effects that weren’t practical with OnGUI. The only probl