html - Floating element with 100% height -

I have an element (shown as one side) that I need to extend the full height of the page is. However, the height is visible to be ineffective with "height 100%".

Here's the bella:

  one side {width: 300px; Swim left; Background color: # 808,080; Height: 100%; }    
 
 
 add it  
  html {height: 100} %; }