screenshot of the problem scrolling
Example:
<link href="https://stackpath.bootstrapcdn.com/bootstrap/4.4.1/css/bootstrap.css" rel="stylesheet"/>
<div class="d-flex overflow-hidden" style="max-width:200px; max-height:200px;">
<div class="d-flex flex-column flex-fill bg-warning overflow-hidden">
<div class="d-flex flex-fill bg-success"></div>
<div class="d-flex flex-shrink-0 overflow-auto">
<div class="p-2 border border-light text-light" style="width: 40px; height:40px;">abc</div>
<div class="p-2 border border-light text-light" style="width: 40px; height:40px;">abc</div>
<div class="p-2 border border-light text-light" style="width: 40px; height:40px;">abc</div>
<div class="p-2 border border-light text-light" style="width: 40px; height:40px;">abc</div>
<div class="p-2 border border-light text-light" style="width: 40px; height:40px;">abc</div>
<div class="p-2 border border-light text-light" style="width: 40px; height:40px;">abc</div>
<div class="p-2 border border-light text-light" style="width: 40px; height:40px;">abc</div>
<div class="p-2 border border-light text-light" style="width: 40px; height:40px;">abc</div>
</div>
</div>
<div class="d-flex flex-column flex-shrink-0 bg-dark overflow-auto">
<div class="p-2 border border-light text-light" style="width: 40px;">abc</div>
<div class="p-2 border border-light text-light" style="width: 40px;">abc</div>
<div class="p-2 border border-light text-light" style="width: 40px;">abc</div>
<div class="p-2 border border-light text-light" style="width: 40px;">abc</div>
<div class="p-2 border border-light text-light" style="width: 40px;">abc</div>
<div class="p-2 border border-light text-light" style="width: 40px;">abc</div>
<div class="p-2 border border-light text-light" style="width: 40px;">abc</div>
<div class="p-2 border border-light text-light" style="width: 40px;">abc</div>
</div>
</div>
https://jsfiddle.net/p6khs5q9/
Basically, I've got myself a vertical flex container with items (not fixed sized, the right bar in the example) when the content is large enough for it to become scroll-able the scroll bar overlaps the container rather than increase the width of the container, but this problem is only apparent in the vertical bar, in the same example I got the horizontal container where it vertically expands the container to accommodated the scrollbar when resized.
I'm not sure whats going wrong as logically it should just expand to accommodate the extra content but it seems the scrollbar defy the laws of MY logic :p
I would appreciate any feedback or hints on this matter as I'm at a lost.
Edit: updated the fiddle to set max-width/height, also I'm looking for a cross browser solution as chrome seem to work sometimes but IE/Edge/FF show the wrong behaviour, I've added a screenshot of the actual problem where the content is being overlapped squeezed rather than pushed out.