Generally speaking styling scrollbars is a bit tricky as each browser has its own way of doing it. Here’s how to do it in webkit (chrome, opera).

.dashed-slug-wallets-exchange table::-webkit-scrollbar {
    width: 0.5em;
}

.dashed-slug-wallets-exchange table::-webkit-scrollbar-thumb {
  background-color: rgba(255,255,0,0.5);
}

The above will make the scrollbars yellow semi-transparent. You can read more about the topic here: https://css-tricks.com/almanac/properties/s/scrollbar/

with regards