Can you have 3 values for margin? I thought it was either two values (top/bottom left/right) or all four.

Also, instead of the comment, I'd extract an SCSS variable:

```scss
$footer-height: 100px;
body {
  margin: 0 0 $footer-height;
}

....

.footer-2 {
  ....
  height: $footer-height;
}
```