title: How to show scrollbar on mouse over?
body: <p>If you go to <a href="https://www.youtube.com/" rel="noreferrer">youtube</a>, you can see how their sidebar scrollbar becomes visible as soon as your mouse moves over it. I've been trying to replicate this, but my div only shows the scrollbar once I start actually scrolling.</p>
  <p>I have <code>overflow-y: auto;</code>, but I've also tried it with <code>overflow-y: scroll;</code>, which had the same effect.</p>
  <p>How can I make the scrollbar visible right away?</p>