Hi,

Please go to Appearance → Customize → Custom CSS then add the following custom CSS code:

:root {
  --mainColor: #ff9800;
}
.post-entry a {
  background:
     linear-gradient(
       to bottom,
       var(--mainColor) 0%,
       var(--mainColor) 100%
     );
  background-position: 0 100%;
  background-repeat: repeat-x;
  background-size: 4px 4px;
  color: #000;
  text-decoration: none;
  transition: background-size .2s;
}
.post-entry a:hover {
  background-size: 4px 50px;
}

Regards,
PenciDesign.