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

I know it's been a looong time since the question was made, but I found an easy solution and thought someone could use it (sorry about the poor english). Here it goes:

CSS

.main, .sidebar {
    float: none;
    padding: 20px;
    vertical-align: top;
}
.container {
    display: table;
}
.main {
    width: 400px;
    background-color: LightSlateGrey;
    display: table-cell;
}
.sidebar {
    width: 200px;
    display: table-cell;
    background-color: Tomato;
}

HTML

    

        simple text here
    
    

        Lorem ipsum dolor sit amet, consectetur adipiscing elit. Etiam congue, tortor in mattis mattis, arcu erat pharetra orci, at vestibulum lorem ante a felis. Integer sit amet est ac elit vulputate lobortis. Vestibulum in ipsum nulla. Aenean erat elit, lacinia sit amet adipiscing quis, aliquet at erat. Vivamus massa sem, cursus vel semper non, dictum vitae mi. Donec sed bibendum ante.
    

Simple example. Note that you can turn into responsiveness.