Flexbox padding bottom fails in Firefox and Safari - css

Question

When scrolling down the .parent div you should see its red background at the bottom due to the padding-bottom. This works in Chrome, but not in Safari and Firefox.
.container {
display: flex;
width: 200px;
height: 500px;
}
.parent {
display: flex;
flex-direction: column;
background: red;
padding-top: 20px;
padding-bottom: 20px;
overflow: auto;
flex: 1;
}
.child {
flex: 1 0 100px;
background: green;
border: 1px solid blue;
}
<div class="container">
<div class="parent">
<div class="child">
child
</div>
<div class="child">
child
</div>
<div class="child">
child
</div>
<div class="child">
child
</div>
<div class="child">
child
</div>
<div class="child">
child
</div>
<div class="child">
child
</div>
</div>
</div>
codepen: http://codepen.io/anon/pen/NpvJPY
Edit: This question is different from the proposed duplicate because it regards a problem with a fixed padding in pixels, as opposed to the percentage padding in the duplicate.

Answer 1

I'm not exactly sure why the padding-bottom fails in Firefox and Safari. It may have something to do with the container being over-constrained. But that's just a guess.
What I am more certain about, however, is a reliable, cross-browser solution. Pseudo-elements on a flex container are rendered as flex items. So instead of padding use ::before and ::after.
.container {
display: flex;
width: 200px;
height: 500px;
}
.parent {
display: flex;
flex-direction: column;
background: red;
/* padding-top: 20px; */
/* padding-bottom: 20px; */
overflow: auto;
flex: 1;
}
/* NEW */
.parent::before,
.parent::after {
flex: 0 0 20px;
content: '';
}
.child {
flex: 1 0 100px;
background: green;
border: 1px solid blue;
}
<div class="container">
<div class="parent">
<div class="child">child</div>
<div class="child">child</div>
<div class="child">child</div>
<div class="child">child</div>
<div class="child">child</div>
<div class="child">child</div>
<div class="child">child</div>
</div>
</div>
revised codepen