what is ::after ::before pseudo elements code example

Example 1: after element is blocking

.select:after {
    position:absolute;
    bottom:.15em;
    top:.15em;
    right:.5rem;
    content:'\2193';
    pointer-events: none;
}

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;
}