.opacity30 { opacity: 0.3; filter: alpha(opacity=30); /* For IE8 and earlier */ }
background: rgba(255, 255, 255, 0.25);
h1 {background-color:rgba(255,0,0,0.3);}
rgba(51, 170, 51, .1) /* 10% opaque green */ rgba(51, 170, 51, .4) /* 40% opaque green */ rgba(51, 170, 51, .7) /* 70% opaque green */ rgba(51, 170, 51, 1) /* full opaque green */