css - How to prevent background color of a body tag from spilling onto it's margin -

I am writing a very simple CSS code which is listed below:

  body {Background color: # 616,161; Margin-left: 20%; }   
 However I have specified 20% margin on the left, background color also affects the marginal area of ​​body tag. How do I ensure that the background color remains within range?   
 
 
 In background color  
    
 Then use this CSS to specify the color and the margin, you will need to zoom the code to get the width and height, where you want  
  html {height: 100%; Body {height: 100%; Margin top: 0px; Margin-left: 20%; }. Background {min-height: 100%; Height: auto; Background color: # 616,161; Width: 100%; }   
 Or as Miro pointed out:  
  html {background-color: #fff; } Body {background-color: # 616161; Margin: 0% 0% 0% 20%; }