How to change color and size of right scrollbar width?

You can use the ::webkit-scrollbar selector. Below is an example, but the link has much more!
Just place this code in userstyle.css (and userchrome.css if you want it on all scrollbars)

::-webkit-scrollbar {
	width: 20px;
}
::-webkit-scrollbar-thumb {
    background-color: white;
}

There is a wiki for sharing customizations as well as a thread for sharing. The wiki includes a link with an introduction on how to discover css classes to target for customization, but ultimately you'll need to either know css or refer to customizations that people share.

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