css ::after with html? code example

Example 1: how use befor after for image

/* for child  */

.custom_img:after {
    content: "";
    background-color: #2359cf;
    height: 400px;
    width: 70%;
    top: -15px;
    right: -6px;
    position: absolute;
    z-index: 999;
}

Example 2: after in css

span[data-descr] {
  position: relative;
  text-decoration: underline;
  color: #00F;
  cursor: help;
}

span[data-descr]:hover::after,
span[data-descr]:focus::after {
  content: attr(data-descr);
  position: absolute;
  left: 0;
  top: 24px;
  min-width: 200px;
  border: 1px #aaaaaa solid;
  border-radius: 10px;
  background-color: #ffffcc;
  padding: 12px;
  color: #000000;
  font-size: 14px;
  z-index: 1;
}