<!DOCTYPE html>
<style>
::-webkit-scrollbar {
    width: 30px;
    height: 30px;
}
::-webkit-scrollbar-thumb {
    background: green;
}
#scroller {
    overflow: scroll;
    width: 400px;
    height: 400px;
}
#space {
    width: 1200px;
    height: 900px;
}
</style>
<div id="scroller"><div id="space"></div></div>