add opacity to background image tool code example

Example 1: set background image opacity

#bg{
background-image: url('images/wood1.jpg');
opacity:0.2;
width:300px;
height:300px;
}

Example 2: background image opacity css

/* Two ways to make images opaque */

div {
	background-color : rgba(120, 120, 120, 0.5) 
   	/* the 0.5 is the value of opacity on a scale of 0-1 */
}

/* OR */

div {
	background-color : blue
    opacity : 50%
}

Example 3: Background image opacity CSS

div {
    opacity : 50%;
}

/* Use opacity to change the opacity of selected css */