CODE EXAMPLE FOR CSS

title underline

h1 {
  display: inline-block;
  position: relative;
}
h1::after {
  content: '';
  position: absolute;
  left: 10%;
  display: inline-block;
  height: 1em;
  width: 70%;
  border-bottom: 1px solid;
  margin-top: 5px;
}