How to change pseudo classes ? Urgent!

Hi,

i am trying to change a pseudo class with puzzles – without success. May someone point me to the right direction ?

my pseudo class is:

.slider::-webkit-slider-thumb {
-webkit-appearance: none;
appearance: none;
width: 80px;
height: 485px;
background: rgba(0, 0, 0, 0);
background-image: url(‘images/slider_handle_d_p.png’);
opacity: 1.0;
cursor: pointer;

and i want to change the background-image. what is the correct way to select the pseudo-class ?