You can change whatever you like. Simply throw the appropriate CSS before </style>. 

::-webkit-scrollbar-thumb:vertical {
background-color: SCROLLBAR FACE COLOR;
height: 30px;}
 
::-webkit-scrollbar {
height: 30px;
width: 6px;
background-color: SCROLLBAR BACKGROUND COLOR;}

You can find other customization options through a google search. Although I recently have not been adding scrollbar options because things have been messing up with Chrome.