一、实现如下图所示上下跳动特效

二、废话少说，直接上代码

    <div class="main-arrow">
          <div class="main-arrow-icon ignore"></div>
     </div>

.main-arrow {
  position: absolute;
  bottom:1.2vw;
  left: 50%;
  z-index: 2;
  margin-left:-3.73vw;
  width:7.46vw;
  height:7.46vw;
  font-size: 0;
  -webkit-animation: down 1.2s cubic-bezier(.25,.1,.25,.1) infinite;
  animation: down 1.2s cubic-bezier(.25,.1,.25,.1) infinite;
}
.main-arrow-icon {
  width: 100%;
  height: 100%;
  transform: rotate(135deg);
  overflow: hidden;
}
.main-arrow-icon:before {
  width:3.7vw;
  height:3.7vw;
}
.main-arrow-icon.ignore:before,.main-arrow-icon.ignore:after {
  border-left:2px solid #fff;
  border-bottom:2px solid #fff;
}
.main-arrow-icon:after {
  margin-left:0.8vw;
  margin-top:-0.8vw;
  width:2.4vw;
  height:2.4vw;
}
.main-arrow-icon:after, .main-arrow-icon:before {
     position: absolute;
     content: "";
     left: 50%;
     top: 50%;
     transform: translate(-50%,-50%);
}
@keyframes down{
  0% {
    bottom:1.2vw;
  }
  50% {
   bottom: 2.8vw;
  }
  100%{
   bottom:1.2vw;
  }
}