<div class="button">My Button</div>
<div><a href="https://www.sitepoint.com/community/t/css-hover-with-background-image-not-working/368076?u=sama74">https://www.sitepoint.com/community/t/css-hover-with-background-image-not-working/368076?u=sama74</a></div>

.button {
  position: relative;
  max-width: 66em;
  padding: 15px;
  background: rgba(0, 100, 250, 1);
  color: white;
  border-radius: 7px;
  margin-bottom: 35px;
  transition: 2s;
}
.button:hover {
  background: rgba(0, 100, 250, 0);
}
.button::before {
  content: "";
  position: absolute;
  top: 0;
  bottom: 0;
  left: 0;
  right: 0;
  z-index: -1;
  background-image: linear-gradient(
    to right top,
    #2525a7,
    #222299,
    #1f1f8b,
    #1c1c7d,
    #191970
  );
  border-radius: 7px;
}