.anim-underline01 {
  position: relative;
}

.anim-underline01::before {
  content:"";
  position: absolute;
  top: 0;
  bottom: 0;
  left: 0;
  right: 0;
  background: linear-gradient(transparent 40%, #f5ff00 60%);
  animation: underlineAnim 2s ease-in infinite;
  z-index: -1;
}

@keyframes underlineAnim {
  0% {
    right: 100%;
  }
  100% {
    right: 0;
  }
}