transparent background css

.opacity30 {
  opacity: 0.3;
  filter: alpha(opacity=30); /* For IE8 and earlier */
}img {
  opacity: 0.5;
} img {
  opacity: 0.5;
}body {
  background: #ffffff url("img_tree.png") no-repeat fixed right top;
}html,body {
  background-color: red;
}div {
  width: 200px;
  height: 200px;
  display: block;
  position: relative;
}

div::after {
  content: "";
  background: url(image.jpg);
  opacity: 0.5;
  top: 0;
  left: 0;
  bottom: 0;
  right: 0;
  position: absolute;
  z-index: -1;   
}