Don't use opacity
for this, set the background to an RGBA-value instead to only make the background semi-transparent. In your case it would be like this.
.content {
padding:20px;
width:710px;
position:relative;
background: rgb(204, 204, 204); /* Fallback for older browsers without RGBA-support */
background: rgba(204, 204, 204, 0.5);
}
See http://css-tricks.com/rgba-browser-support/ for more info and samples of rgba-values in css.