You need to specify the z-index
to change the natural stacking order of elements positioned anything other than static
.
So I added a value of 1 for the z-index
here:
#slider::-webkit-slider-thumb {
-webkit-appearance: none;
width: 10px;
height: 85px;
background: black;
position: fixed;
top: 10px;
left: 120px;
z-index: 1;
}
Forked your fiddle here.