Just a Scroll Bar

Problem - Add on suddenly will not save settings

When I first installed this, it allowed me to choose a custom theme (I liked Edgy Blue) and then it allowed me to change the width and height of the scrollbars using Edgy Blue. Suddenly, I cannot change the size of the Edgy Blue scrollbar. When I try, it reverts back to the plain faded blue bar. How can I fix this?