Messing around Customize buttons

Hey, thank you for this amazing plugin! It’s saving me in many ways (^o^).

I’m not really used to work with coding so that’s maybe the reason I’m messing around with this. I’m trying to change borders and colors of buttons. I’ve achieved to change background color when mouse is over typing what you’ll see below, but doing the same doesn’t work with the border that stays red. Same case with selected, no matter what I write in style box, it’s still red.

.ButtonSelectorItem:hover
{background-color: #dcdcdc;
}

Is this a premium option or am I doing it wrong?

Thanks for your time!