html – css透明形状覆盖图像

div {
  position: relative;
  height: 300px;
  width: 500px;
  BACkground: url(http://lorempixel.com/500/300);/*image path*/
  overflow: hidden;/*hides the rest of the circle*/
}

div:before {
  content: "";
  position: absolute; /*positions with reference to div*/
  top: 100%;
  left: 50%;
  width: 0;/*define value if you didn't want hover*/
  height: 0;
  border-radius: 50%;
  BACkground: tomato;/*could be rgba value (you can remove opacity then)*/
  opacity: 0.5;
  transform: translate(-50%,-50%);/*ensures it is in center of image*/
  transition: all 0.4s;
}


/*Demo Only*/
div:hover:before {/*place this in your pseudo declaration to remove the hover*/
  height: 100%;
  width: 150%;/*this makes the shape wider than square*/
  transform: translate(-50%,-50%) rotate(5deg);/*ensures it is in center of image + rotates*/
}
div {/*This stuff is for the text*/
  font-size: 40px;
  line-height: 300px;
  text-align: center;
}

<div>HOVER ME</div>