How can I make a div 100% of window height?

Question

I just want to have a sidebar that will be 100% of window height, but nothing works except this:

#sidebarBack {
background: rgba(20, 20, 20, .3);
position: f         


        

Answer 1

Try this -

html,body{height:100%;}
#sidebar {
background: rgba(20, 20, 20, .3);
/*position: fixed;*/
width: 100px;
height: 100%;
left: 0;
float:left;
}


section#settings {
width: 62%;
height: auto;
display: inline-block;
position: relative;
margin-left: 100px;
float:left;
}

​