Align an element to bottom with flexbox

Question

I have a div with some children:

<div class="content">
  <h1>heading 1</h1>
  <h2>heading 2</h2>
  <p>Some more or less text</p>
  <a href="/" class="button">Click me</a>
</div>

and I want the following layout:

 -------------------
|heading 1          |
|heading 2          | 
|paragraph text     |
|can have many      |
|rows               |
|                   |
|                   |
|                   | 
|link-button        |
 -------------------

Regardless how much text is in the p I want to stick the .button always at the bottom without taking it out of the flow. I've heard this can be achievable with Flexbox but I can't get it to work.

Answer 1

You can use auto margins

Prior to alignment via justify-content and align-self, any positive free space is distributed to auto margins in that dimension.

So you can use one of these (or both):

p { margin-bottom: auto; } /* Push following elements to the bottom */
a { margin-top: auto; } /* Push it and following elements to the bottom */

.content {
  height: 200px;
  border: 1px solid;
  display: flex;
  flex-direction: column;
}
h1, h2 {
  margin: 0;
}
a {
  margin-top: auto;
}

<div class="content">
  <h1>heading 1</h1>
  <h2>heading 2</h2>
  <p>Some text more or less</p>
  <a href="/" class="button">Click me</a>
</div>

Alternatively, you can make the element before the a grow to fill the available space:

p { flex-grow: 1; } /* Grow to fill available space */

.content {
  height: 200px;
  border: 1px solid;
  display: flex;
  flex-direction: column;
}
h1, h2 {
  margin: 0;
}
p {
  flex-grow: 1;
}

<div class="content">
  <h1>heading 1</h1>
  <h2>heading 2</h2>
  <p>Some text more or less</p>
  <a href="/" class="button">Click me</a>
</div>