this is also easy to use..
how to make the background, and the top menus have opacity.
your going to add this to your /templates/_header.html at the end..
Please change the image link to yours and your good to go.
<style>body{background: url("http://www.mynewbeetle.net/photos/bkg1.jpg") Top Center no-repeat;background-attachment:fixed; background-color:#ffffff;}
.page_block_container{filter:alpha(opacity=99); -moz-opacity:0.990; -khtml-opacity: 0.990; opacity: 0.990;}
div.sys_top_menu{filter:alpha(opacity=90); -moz-opacity:0.90; -khtml-opacity: 0.90; opacity: 0.90;}
div.sys_main_logo {background: rgba(255, 255, 255, 0.7)}
.page_block_container {background-color:#fff;background: rgba(255, 255, 255, 0.99)}
div.dbContent{background-color:#fff;background: rgba(255, 255, 255, 0.99)}
</style>Clean your cache and you should be good....
Have fun!