How do I give text or an image a transparent background using CSS?

p {
  position: absolute;
  background-color: green;
  filter: alpha(opacity=60);
  opacity: 0.6;
}

span {
  color: white;
  filter: alpha(opacity=100);
  opacity: 1;
}

<p>
  <span>Hello world</span>
</p>

Answer: 

background-color:rgba(255,0,0,0.5);

CSS background-image Property

CSS background-image Property

syntax 

background-image: url("image path");

single background image set Example code

<style>

body  {

           background-image: url("backgroundimage.gif");

         }

</style>

Multiple background images set Example code

<style>

body {

            background-image: url("backgroundimage1.png"), url("backgroundimage2.jpg");

         }

</style>