How to center an element vertically in css in a scrollable container - html

Question

I am trying to center an element vertically inside a parent element using css. The parent element has a dynamic height and I would like the parent box to scroll if the height of the parent is less than the height of the child. I tried using flex boxes and the transform: translate technique described here (https://css-tricks.com/quick-css-trick-how-to-center-an-object-exactly-in-the-center/) to center the child. Both techniques worked, but resulted in strange scrolling behavior when the parent gets too small.
#wrapper {
top: 0;
bottom: 0;
left: 0;
right: 0;
overflow: auto;
position: absolute;
}
.center {
width: 200px;
height: 200px;
background-color: yellow;
position: absolute;
top: 50%;
left: 50%;
-webkit-transform: translate(-50%, -50%);
transform: translate(-50%, -50%);
-webkit-transform: translate(-50%, -50%);
}
Here is a jsfiddle that shows what I mean: http://jsfiddle.net/snhpdL91/
Notice that if you scale the window down until the scroll bars appear the text "hello" at the top of the child is cut off, even when scrolled to the very top. How can I make it so that I can scroll across the full range of the child element?

Answer 1

You can use flexbox with auto margins:
Prior to alignment via justify-content and align-self,
any positive free space is distributed to auto margins in that
dimension.
It works because only positive free space is distributed.
#wrapper {
display: flex;
}
.center {
margin: auto;
}
#wrapper {
top: 0;
bottom: 0;
left: 0;
right: 0;
overflow: auto;
position: absolute;
display: flex;
}
.center {
width: 300px;
height: 300px;
background-color: yellow;
margin: auto;
}
<div id="wrapper">
<div class="center">Hello</div>
</div>