My position: sticky element isn't sticky when using flexbox

Question

I was stuck on this for a little bit and thought I'd share this position: sticky + flex box gotcha:

My sticky div was working fine until I switched my view to a flex box container, and suddenly the div wasn't sticky when it was wrapped in a flex box parent.

.flexbox-wrapper {
  display: flex;
  height: 600px;
}
.regular {
  background-color: blue;
}
.sticky {
  position: -webkit-sticky;
  position: sticky;
  top: 0;
  background-color: red;
}

<div class="flexbox-wrapper">
  <div class="regular">
    This is the regular box
  </div>
  <div class="sticky">
    This is the sticky box
  </div>
</div>

JSFiddle showing the problem

Answer 1

Since flex box elements default to stretch, all the elements are the same height, which can't be scrolled against.

Adding align-self: flex-start to the sticky element set the height to auto, which allowed scrolling, and fixed it.

Currently this is only supported in Safari and Edge

.flexbox-wrapper {
  display: flex;
  overflow: auto;
  height: 200px;          /* Not necessary -- for example only */
}
.regular {
  background-color: blue; /* Not necessary -- for example only */
  height: 600px;          /* Not necessary -- for example only */
}
.sticky {
  position: -webkit-sticky;
  position: sticky;
  top: 0;
  align-self: flex-start; /* <-- this is the fix */
  background-color: red;  /* Not necessary -- for example only */
}

<div class="flexbox-wrapper">
  <div class="regular">
    This is the regular box
  </div>
  <div class="sticky">
    This is the sticky box
  </div>
</div>

JSFiddle showing the solution