It really depends on browsers.
With pure css, for simple changes like witdh and colors, you could try with
::-webkit-scrollbar {
width: 14px;
background-color: silver;
}
::-webkit-scrollbar-track {
-webkit-box-shadow: inset 0 0 6px rgba(0,0,0,0.3);
border-radius: 10px;
background-color: silver;
}
::-webkit-scrollbar-thumb {
border-radius: 10px;
-webkit-box-shadow: inset 0 0 6px rgba(0,0,0,0.5);
background-color: #0099cc;
}
but it wont work in all browsers, like Firefox. For that you will have to use JS, jquery based scrollbars like jscrollpane YIu could also check https://codemug.com/html/custom-scrollbars-using-css/ for more CSS solutions.