<div class="opacity-demo">
   <p style="background-color: rgba(100,100,100,1)">Opacity of 1
   </p>
   <p style="background-color: rgba(100,100,100,0.75)">Opacity of 0.75
   </p>
   <p style="background-color: rgba(100,100,100,0.5)">Opacity of 0.5
   </p>
   <p style="background-color: rgba(100,100,100,0.25)">Opacity of 0.25
   </p>
   <p style="background-color: rgba(100,100,100,0)">Opacity of 0
   </p>
 </div>

In style element (<style>) within head element:

.opacity-demo {
     background-image: url('images/satin.png');
     background-size: cover;
     color: white;
   }
   .opacity-demo p { color: #ffffff; font-size: 200%; font-weight: bold; font-family: helvetica,sans-serif;}