How to change scroll bar properties to a inside iframe

Question

I'm using the following code to change the main scroll bar properties. But I just only need to change the scroll bar properties of an inside iframe in a page. How am I suppose to do that only?

::-webkit-scrollbar {
    width: 6px;
    height: 4px;
    background: #ffffff;
}

::-webkit-scrollbar-thumb {
    background-color: #ea421e;
    -webkit-border-radius: 1ex;
}