feature: Add custom scrollbar

Hi!
Please, do you can change the default scrollbar?

Something like this:

::-webkit-scrollbar {
	height: 5px;
	width: 5px;
	background-color: transparent;
}
::-webkit-scrollbar-thumb {
	border-radius: 0.375rem;
	background-color: #e3e3e3;
}
.application.dark ::-webkit-scrollbar {
	height: 5px;
	width: 5px;
	background-color: transparent;
}
.application.dark ::-webkit-scrollbar-thumb {
	border-radius: 0.375rem;
	background-color: #2e2e2d;
}

All the best.

The issue provides CSS scrollbar selectors but names no project files or tests. First locate the browser UI stylesheet and check how light and dark themes are styled, then verify the custom scrollbar appearance in the supported browsers; done means the default scrollbar matches the requested examples without disrupting the UI.