unity slider not empty
//1. Create a slider
//2. Delete the Handle Slide area (don't need that part for progress / heath bars)
//3. Set the Target Graphic to the Fill GO (child of Fill Area) - else it complains about not having a graphic
//4. (now for the important part)
//5. Set the Slider value to 0 - V.Important before altering anything else
//6. Select the Fill GO and set its width to 0
//7. Select the Fill Area GO and using the Rect Tool (in the editor toolbar) to alter It's Rect to fill the Background graphic (as shown below)