How to stretch flexbox (.container) to full height?

Question

css

I am mastering flexes and I don’t understand how to stretch the .container block to the footer. It is necessary that the .content and .rs blocks fill the entire height https://jsfiddle.net/d8amj3hw/1/

Answer 1

.middle needs to be made flex so that the container inside also stretches https://jsfiddle.net/d8amj3hw/3/