How to force child div to be 100% of parent div's height without specifying parent's height?

Question

I have a site with the following structure:

  

  <         


        
      

Answer 1

.row-eq-height {
display: -webkit-box;
display: -webkit-flex;
display: -ms-flexbox;
display:         flex;
 }

From:

http://getbootstrap.com.vn/examples/equal-height-columns/equal-height-columns.css

states bootstrap but you do not need bootstrap to use this. Answering this old question, as this worked for me, and seems pretty easy to implement.

This was the same answer I provided to this Question