This example defines a thin scrollbar with a red thumb and an orange track. To view the thumb, you will need to scroll the text. After the scrollbar is visible, hover over it to see the track.

.poem {
  width: 300px;
  height: 100px;
  border: 1px solid;
}

css

.poem {
  overflow: scroll;
  scrollbar-color: red orange;
  scrollbar-width: thin;
}

<blockquote class="poem">
  <h3>A Small Needful Fact</h3>
  <pre>
Is that Eric Garner worked
for some time for the Parks and Rec.
Horticultural Department, which means,
perhaps, that with his very large hands,
perhaps, in all likelihood,
he put gently into the earth
some plants which, most likely,
some of them, in all likelihood,
continue to grow, continue
to do what such plants do, like house
and feed small and necessary creatures,
like being pleasant to touch and smell,
like converting sunlight
into food, like making it easier
for us to breathe.
</pre>
  <p>
    - <a href="https://onbeing.org/poetry/a-small-needful-fact/">Ross Gay</a>
  </p>
</blockquote>

Note: When customizing scrollbars, ensure that the thumb and track have enough contrast with the surrounding background. Also ensure that the scrollbar hit area is large enough for people who use touch input.