css实现边框动画

  <div class="box">
    <div class="yespost">Hover</div>
  </div>

  <style>
  #box{
    width: 200px;
    margin: 500px auto;
  }
  .yespost {
  width: 100%;
  height: 80px;
  text-indent:1em;
  cursor: pointer;
  letter-spacing:2px;
  margin: 5px 0;
  background: none;
  border: 0;
  box-sizing: border-box;
  position: relative;
  vertical-align: middle;
  transition: color 0.25s;
}
.yespost::before, .yespost::after {
  box-sizing: inherit;
  content: '';
  position: absolute;
  width: 100%;
  height: 100%;
}
.yespost::before, .yespost::after {
  border: 2px solid transparent;
  width: 0;
  height: 0;
}
.yespost::before {
  top: 0;
  left: 0;
}
.yespost::after {
  bottom: 0;
  right: 0;
}
.yespost:hover {
  color: #69b7ff;
}
.yespost:hover::before, .yespost:hover::after {
  width: 100%;
  height: 100%;
}
.yespost:hover::before {
  border-top-color: #69b7ff;
  border-right-color: #69b7ff;
  transition: width 0.25s ease-out, height 0.25s ease-out 0.25s;
}
.yespost:hover::after {
  border-bottom-color: #69b7ff;
  border-left-color: #69b7ff;
  transition: border-color 0s ease-out 0.5s, width 0.25s ease-out 0.5s, height 0.25s ease-out 0.75s;
}

.yespost div:nth-child(1){
  font-size: 17px;
  font-weight: 600;
  font-family: "Arial","Microsoft YaHei","黑体","宋体","sans-serif";
  padding-top: 17px;
  margin-bottom: 2px;
}
.yespost div:nth-child(2){
  font-size: 12px;
}
.background{
  background-color: #69b7ff;
  color: #FFFFFF;
}
.yespostHober:hover{
  color: #FFFFFF;
}
  </style>