html - How to stretch flex child to fill height of the container?

Question

I need to stretch yellow child to fill all height of parent. Without setting parent height. Height of parent should be dependent on blue child text. https://jsfiddle.net/7vaequ1c/1/

<div style='display: flex'>
  <div style='background-color: yellow;height: 100%; width: 20px'>
  </div>
  <div style='background-color: blue'>
  some<br>
  cool<br>
  text
  </div>
</div>

Answer 1

When using Flexbox, the major mistake is to start using height: 100% all over.

We are used to that in many cases, though when it comes to Flexbox, it often breaks it instead.

The solution is simple, just remove the height: 100%, and it will work automatically.

The reason it does, is for flex item in row direction (the default), the align-items control the vertical behavior, and as its default is stretch this just work as is.

Stack snippet

<div style='display: flex'>
  <div style='background-color: yellow; width: 20px'>
  </div>
  <div style='background-color: blue'>
    some<br> cool<br> text
  </div>
</div>