Describe the feature/addition!

I set up an Sphax 128x extension pack for Techopolis 3 and the GUI uses an oversized slider:

Would be great, if that slider image could be overloaded with an 16x version by me. (Or at least a hint what generic image is used here, so that I can remove/overwrite it in resource pack.)

Why would like to see this feature/addition?

Would looks better in Sphax ....