css transparent background color

1/* Use RGBA */
2background-color: rgba(255, 255, 0, 0.75); /* Transparent Yellow */

1div {
2	background: transparent
3}

1body {
2  background-color: rgb(255,255,255);
3}

1.opacity30 {
2  opacity: 0.3;
3  filter: alpha(opacity=30); /* For IE8 and earlier */
4}

1html,body {
2  background-color: red;
3}

1div {
2 opacity:25% ; 
3}