Flex sidebar: how to grow to 100% of height

Question

I´m building a sidebar using CSS flex and I need it to grow vertically to fill the whole screen vertical height. Here is a skeleton of what I´m doing.

JSFiddle here

Answer 1

body, html {
  height: 100%;
}

And the fiddle https://jsfiddle.net/gxkezny9/

One of the parent containers wasn't 100% height