#glowing-span.glowing-span {
  position: relative;
  display: inline-block;
  font-size: 1.5em;
  font-weight: bold;
  text-transform: uppercase;
  letter-spacing: 2px;
}
#glowing-span.glowing-span:before {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background: linear-gradient(45deg, #ff00ff, #ffcc00);
  z-index: -1;
  border-radius: inherit;
  animation: glowAnimation 5s infinite alternate;
}

@keyframes glowAnimation {
  0% {
    background: linear-gradient(45deg, #ff00ff, #ffcc00);
  }
  100% {
    background: linear-gradient(45deg, #00ff00, #ffcc00);
  }
}