title: Scrolling a dropdown in a modal in Bootstrap4
body: <p>I'm currently migrating from Bootstrap4 alpha to Bootstrap4 stable. So far, so good, except this problem I have with my modals. I'm using dropdowns everywhere, including ones with many items. Previously, the scrolling was working perfectly. Now it does not: when I scroll, this is the modal filter (.modal-backdrop) that is scrolling, and not the dropdown's list.</p>
  
  <p>Here is a full page example:</p>
  
  <p><a href="https://www.codeply.com/go/JKlWFeOgtU" rel="nofollow noreferrer">https://www.codeply.com/go/JKlWFeOgtU</a></p>