I can’t understand ho I can replicate this effect on button, like in this theme:(scroll below and look where button say "read more") https://hiroshi.qodeinteractive.com

my button class: border-button

    .border-button {
  font-family: "Montserrat";
  display: inline-block;
  text-decoration: none;
  position: relative;
  padding: 12px 8px;
  color: #000;
  overflow: hidden;
}

.border-button::before {
  content: "";
  color: black;
  position: absolute;
  bottom: 0;
  left: 0;
  width: 100%;
  height: 1px;
  background-color: #000;
  transform: translateX(-100%);
  transition: transform 0.4s ease-out;
}

.border-button:hover::before {
  color: black;
  transform: translateX(0);
}
a:hover{
    color: black;
}

>Solution :

CSS transition allows you to change property values smoothly, over a given duration.

Try using the transition property with background properties like this:

.myanime {
  cursor: pointer;
  background-image: linear-gradient(to right, #000 33%,#0000 33% 66%,#000 66%);
  background-position: right bottom;
  background-size: 300% 2px;
  background-repeat: no-repeat;
}

.myanime:hover {
  background-position: left bottom;
  transition: background-position 1s;
}

<span class="myanime">read more</span>