<a href="#" class="example">
  <figure>
    <img src="https://www.ameamelog.com/wp/wp-content/uploads/2019/08/css-scale_dummy.jpg" alt="">
    <figcaption>Example</figcaption>
  </figure>
</a>

body {
  min-height: 100vh;
  margin: 0;
  padding: 0;
  display: flex;
  justify-content: center;
  align-items: center;
}
img {
  vertical-align: bottom;
}

.example {
  color: #fff;
  display: flex;
  justify-content: center;
  align-items: center;
  position: relative;
}
.example::before {
  content: "";
  width: 100%;
  height: 100%;
  background: -moz-linear-gradient(-90deg, #000000 0%, #000000 25%, #EE9AE5 50%, #5961F9 75%, #FF52E5 100%);
  background: -webkit-linear-gradient(-90deg, #000000 0%, #000000 25%, #EE9AE5 50%, #5961F9 75%, #FF52E5 100%);
  background: linear-gradient(90deg, #000000 0%, #000000 25%, #EE9AE5 50%, #5961F9 75%, #FF52E5 100%);
  background-size: 400% 400%;
  background-repeat: no-repeat;
  display: block;
  position: absolute;
  top: 0;
  left: 0;
  z-index: 2;
  opacity: .5;
  transition: .5s;
}
.example:hover::before {
  background-position: 100% 100%;
}
.example figure {
  margin: 0;
  position: relative;
}
.example figcaption {
  font-size: 24px;
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  z-index: 3;
}