Was talking to someone about CSS Nostalgia and "back in my day" when scrollbar colors came up.
/* For Chromium based browsers */
::-webkit-scrollbar {
background: #2A365F;
}
::-webkit-scrollbar-thumb {
background: #514763;
}
/* For Firefox */
html {
scrollbar-color: #514763 #2A365F;
}
Firefox and Chrome have different selectors, so in order to support the majority of browsers, you need both.