How to reduce the scroll bar width in collection widget

try this CSS... it will be applicable for entire page 

/* width */
::-webkit-scrollbar {
width: 5px;
}
/* Track */
::-webkit-scrollbar-track {
box-shadow: inset 0 0 5px grey;
border-radius: 5px;
}
/* Handle */
::-webkit-scrollbar-thumb {
background: red;
border-radius: 5px;
}