.box {
  position: relative;  
  background: linear-gradient(235deg, #89ff00, #010615, #00bcd4);
}

.box::before {
  content: '';
  position: absolute;
  top: -2px;
  left: -2px;
  right: -2px;
  bottom: -2px;
  z-index: 0;
  filter: blur(40px);
  background: linear-gradient(235deg, #89ff00, #010615, #00bcd4);
  animation: anim 2s linear infinite;
}

.box::after {
  content: '';
  position: absolute;
  top: -2px;
  left: -2px;
  right: -2px;
  bottom: -2px;
  z-index: 1;
  background: linear-gradient(rgba(0, 0, 0, 0.5),rgba(0, 0, 0, 0.5)), url('img/onlinebo.jpg');
  background-position: center;
  background-repeat: no-repeat;
  background-size: cover;
  border-radius:10px;
  border: 5px solid greenyellow;
}
@keyframes anim {
  0%,100% {
    opacity: 1;
  }
  50% {
    opacity: 0;
  }
}