html {
	
	  background: url(chalkboard.jpg) no-repeat center center fixed; 
  -webkit-background-size: cover;
  -moz-background-size: cover;
  -o-background-size: cover;
  background-size: cover;
	
}

.content {
        width: 800px;
        height: 364px;

        position:absolute; /*it can be fixed too*/
        left:0; right:0;
        top:0; bottom:0;
        margin:auto;

        /*this to solve "the content will not be cut when the window is smaller than the content": */
        max-width:100%;
        max-height:100%;
        overflow:auto;
    }
    
    .content img {
	max-width: 100%;
}