.portfolio-container {
  background: -moz-linear-gradient(-45deg, #000000 0%, #000000 25%, #1e539e 50%, #ff3083 75%, #7800a8 100%);
  /* FF3.6-15 */
  background: -webkit-linear-gradient(-45deg, #000000 0%, #000000 25%, #1e539e 50%, #ff3083 75%, #7800a8 100%);
  /* Chrome10-25,Safari5.1-6 */
  background: linear-gradient(135deg, #000000 0%, #000000 25%, #1e539e 50%, #ff3083 75%, #7800a8 100%);
  /* W3C, IE10+, FF16+, Chrome26+, Opera12+, Safari7+ */
  background-size: 400% 400%;
  background-repeat: no-repeat;
  cursor: pointer;
  transition: 0.5s all;
}
.portfolio {
  border:  none;
  background: #ffffff no-repeat center center;
  background-size: cover;
  width: 100%;
  height: 100%;
  z-index: 1;
  opacity: 0.5;
  mix-blend-mode: screen;
}
.portfolio-container:hover {
  background-position: 100% 100%;
}