有什么办法限制边框长度吗？

希望这可以帮助：

#mainDiv {  height: 100px;  width: 80px;  position: relative;  border-bottom: 2px solid #f51c40;  background: #3beadc;}#borderLeft {  border-left: 2px solid #f51c40;  position: absolute;  top: 50%;  bottom: 0;}<div id="mainDiv">  <div id="borderLeft"></div></div>