jQuery轮播新风格接下来和prev在第一张和最后一张幻灯片上

I'm very new with jQuery and I use this jQuery carousel. I don't want to use any plugin. But I want to ask how can I make prev button with another style/color, when I am on first slide and how can I make next button with another style/color,, when I am on last slide.I'm very new with jQuery and I use this jQuery