Issue when centering vertically with flexbox when heights are unknown

Question

My layout has a container flex-container and a child.

HTML:

  
text
<         


        
                      

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Answer 1

I found the solution:

.flex-container {
    display: flex; /* only */
    overflow-y: scroll;
}

.flex-container > div {
    margin: auto; /* horizontal and vertical align */
}

html, body {
    height: 100%;
    width: 100%;
    padding: 0;
    margin: 0;
}

.flex-container {
    display: flex;
    width: 100%;
    height: 100px; /* change height to 300px */
    overflow-y: scroll;
    background: #2a4;
}

.flex-container > div {
    padding: 1em 1.5em;
    margin: auto;
    background: #E77E23;
    width: 400px;
}

<div class="flex-container">
  <div>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Iure fugit voluptas eius nemo similique aperiam quis ut! Ipsa aspernatur rem nesciunt est sed hic culpa nisi delectus error explicabo reprehenderit. Lorem ipsum dolor sit amet, consectetur adipisicing elit. Iure fugit voluptas eius nemo similique aperiam quis ut! Ipsa aspernatur rem nesciunt est sed hic culpa nisi delectus error explicabo reprehenderit. </div>
</div>

Codepen: http://codepen.io/ces/pen/Idklh

Answer 2

Add align-self:flex-start; to .flex-container > div can resolve this problem too.

See: http://www.w3.org/TR/css-flexbox-1/#auto-margins