this Is a basic example of how one would do this:



body{background:url('http://jasonlefkowitz.net/wp-content/uploads/2013/07/Cute-Cats-cats-33440930-1280-800.jpg') no-repeat; background-size:100%; margin:0; overflow:hidden}
header{height:80px;width:100%; background:grey}
#main{width:90%; height:90%; position:absolute; background:rgba(255,255,255,0.5); margin:5%;}
&lt;body&gt;&lt;header&gt;&lt;/header&gt;&lt;div id="main"&gt;&lt;/div&gt;&lt;/body&gt;



Click on the "Full Page" option to see how it would look

In your example you are using background-color:white, with that you could use opacity:0.5 but that would make everything in main translucent. when you want transparencyhtml backgrounds use rgba. 50% transparency white in rgba: background-color:rgba(255,255,255,0.5)

How to center and fill main in html/css?
I'm looking for a word or phrase specifically used to refer to the act of placing a flag to claim new territory. I'm specifically referring to claiming land in the name of some sovereign, though a more general term will do.
