how do i keep centered div with max-width from collapsing when using flexbox column?

Question

I have 3 divs vertically stacked in container. I want middle div to be centered but continue expanding horizontally as much as it can but less than max-width. Just like normal div would with max-width without flexbox involved.

https://codepen.io/anon/pen/XaQXOW

css

.cont {
  display: flex;
  flex-direction: column;
}

.b {
  max-width: 500px;
  background-color: cyan;
}
.a, .b, .c {
  border: 1px solid #000;
  height: 100px;
}

html

<div class="cont">
  <div class="a"></div>
  <div class="b"></div>
  <div class="c"></div>
</div>

Answer 1

Set align-self: center; to center your div and add width: 100%:

.cont {
  display: flex;
  flex-direction: column;
}

.b {
  max-width: 500px;
  background-color: cyan;
  align-self: center;
  width: 100%;
  box-sizing: border-box;
}

.a, .b, .c {
  border: 1px solid #000;
  height: 100px;
}

<div class="cont">
  <div class="a"></div>
  <div class="b"></div>
  <div class="c"></div>
</div>