Make slider hover more distinct?

Where in the code is the slider hover? So I have my sliders set to go to a link when people click on them. At the moment the slider will darken a bit to show that there is a link there, but it's very subtle as my slider images are quite dark. I assume there's something in the CSS where I can either darken that or lighten it so it's more obvious when people move their cursor over the slider, but I can't seem to find the code that does it.