<div class="app">
  <div class="font20">不就是<br>玩嘛！</div>
</div>

.app{
  width: 100%;
  height: 100vh;
  background-color: #ffffff;
  position: relative;
  display: flex;
  justify-content: center;
  align-items: center;
}
.font20{
  color: transparent;
  font-size: 70px;
  font-weight: 900;
  background-image: linear-gradient(-45deg, #fff 0%, #fff 25%, green 25%, green 50%, #fff 50%, #fff 75%, green 75%, green 100%);
  -webkit-background-clip: text;
  animation: font20 10s ease infinite;
}
@keyframes font20{
  0%{
    background-size: 1px 2px;
  }
  20%{
    background-size: 4px 5px;
  }
  40%{
    background-size: 3px 4px;
  }
  60%{
    background-size: 5px 6px;
  }
  80%{
    background-size: 2px 3px;
  }
  100%{
    background-size: 7px 6px;
  }
}