<div>
  <ul class="scroll-shadows">
    <li>Lorem, ipsum.</li>
    <li>Eligendi, repudiandae.</li>
    <li>Dolor, vel.</li>
    <li>Obcaecati, praesentium.</li>
    <li>Impedit, tenetur.</li>
    <li>Exercitationem, repellat!</li>
    <li>Aut, asperiores!</li>
    <li>Dolor, fuga.</li>
    <li>Ab, aliquid!</li>
    <li>Adipisci, totam.</li>
    <li>Error, dicta.</li>
    <li>Saepe, vero?</li>
    <li>Eveniet, dolorem!</li>
    <li>Id, tempora!</li>
    <li>Voluptate, consectetur?</li>
    <li>Voluptatibus, omnis.</li>
    <li>Eius, fugit.</li>
    <li>Quia, non!</li>
    <li>At, laudantium?</li>
    <li>Commodi, maiores!</li>
  </ul>
</div>

.scroll-shadows {
  --bgRGB: 73, 89, 99;
  --bg: rgb(var(--bgRGB));
  --bgTrans: rgba(var(--bgRGB), 0);
  
  --shadow: rgba(41, 50, 56, 0.5);
  
  max-height: 200px;
  overflow: auto;

  background:
    /* Shadow Cover TOP */
    linear-gradient(
      var(--bg) 30%,
      var(--bgTrans)
    ) center top,
    
    /* Shadow Cover BOTTOM */
    linear-gradient(
      var(--bgTrans), 
      var(--bg) 70%
    ) center bottom,
    
    /* Shadow TOP */
    radial-gradient(
      farthest-side at 50% 0,
      var(--shadow),
      rgba(0, 0, 0, 0)
    ) center top,
    
    /* Shadow BOTTOM */
    radial-gradient(
      farthest-side at 50% 100%,
      var(--shadow),
      rgba(0, 0, 0, 0)
    ) center bottom;
  
  background-repeat: no-repeat;
  background-size: 100% 40px, 100% 40px, 100% 14px, 100% 14px;
  background-attachment: local, local, scroll, scroll;
}



/* Not important to the functionality, just for this particular demo */
.scroll-shadows {
  list-style: none;
  padding-right: 0.5rem;
}
.scroll-shadows > * {
  padding: 0.2rem;
}

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}
body {
  background: #455A64;
  color: #CFD8DC;
  height: 100vh;
  display: grid;
  place-items: center;
  font: 500 100% system-ui, sans-serif;
}
.scroll-shadows {
  --scrollbarBG: transparent;
  --thumbBG: #90a4ae;

  scrollbar-width: thin;
  scrollbar-color: var(--thumbBG) var(--scrollbarBG);
}
.scroll-shadows::-webkit-scrollbar {
  width: 6px;
}
.scroll-shadows::-webkit-scrollbar-track {
  background: var(--scrollbarBG);
}
.scroll-shadows::-webkit-scrollbar-thumb {
  background-color: var(--thumbBG);
  border-radius: 6px;
  border: 3px solid var(--scrollbarBG);
}

// just so demo loads scrolled down a little.
// document.querySelector(".scroll-shadows").scrollTop = 100;