brush {
  position: relative;
}

brush::after {
  content: '';
  position: absolute;
  top: 0.5rem;
  bottom: 0rem;
  left: -0.1rem;
  background: #ffde85;
  border-radius: 10% 5% 10% 21%;
  animation: brush 0.3s ease-in-out;
  animation-fill-mode: forwards;
  animation-delay: 500ms;
  z-index: -1;
}

@keyframes brush {
  0% {
    right: 100%;
  }
  10% {
    right: 85%;
  }
  25% {
    right: 65%;
  }
  50% {
    right: 45%;
  }
  75% {
    right: 25%;
  }
  90% {
    right: 5%;
  }
  100% {
    right: 0%;
  }
}