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 the following

#sidebarBack {
 background: rgba(20, 20, 20, .3);
 position: fixed;
 width: 250px;
 top:0;
 bottom:0;
 left: 0;
}