feature: Add custom scrollbar

[lannodev]

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.

[itsgoingd]

Hey, yeah, I want to figure out how to make these look nicer in the next major release redesign.