How to maintain high resolution custom background images for GUI elements on different screen sizes?

Hello everybody,

My team and I are working on a Unity mobile game, the game is supposed to work on different screen sizes and platforms, for example, we're supporting 5" phones and 9.7" tablets.

We're currently replacing GUI elements' backgrounds with our own designed PNG images; our approach is to use high resolution images and scale them down for different screen sizes. We are not sure if this approach is applicable, That's why we're afraid to find out later on that this approach is not as good as we thought it would. My question is not about getting the scaling numbers as it has been answered many times before(by using Screen.width or height). My question is about finding an approach to have high resolution GUI themes on multiple screen sizes.

Just for reference, this is how the code may look:

 highResPNGTexture = Resources.Load("GUI/Buttons/defaultButtonNormal") as Texture2D;
 GUI.skin.button.normal.background = highResPNGTexture;
 //Then create buttons with different sizes
 GUI.Button(new Rect(0, 0, Screen.width / 10, Screen.height / 10), "Small button" );
 GUI.Button(new Rect(0, 0, Screen.width / 4, Screen.height / 4), "Larger button" );

So, to wrap it up, my question is : What is the ideal approach to have high resolution GUI textures on different screen sizes?