You can easily pin a list item to the top of the list using flexbox…

<ul class="List">
  <li class="List__Item">First</li>
  <li class="List__Item">Second</li>
  <li class="List__Item List__Item--Pinned">Pinned</li>
  <li class="List__Item">Last</li>

…by setting the order of the pinned item to -1.

.List {
  display: flex;
  flex-direction: column;

.List__Item--Pinned {
  order: -1;

Beware of the accessibility implications this entails. The order will only change visually, not when navigating through keyboard.