CODE EXAMPLE FOR CSS

fill div on hover

div {
  position: relative;
  display: inline-block;
  padding: 15px 70px;
  border: 5px solid #B17461;
  color: #B17461;
  font-size: 30px;
  font-family: arial;
  background-image: linear-gradient(#B17461, #B17461);
  background-position: 50% 50%;
  background-repeat: no-repeat;
  background-size: 0% 100%;
  transition: background-size .5s, color .5s;
}
div:hover {
  background-size: 100% 100%;
  color: #fff;
}