1像素

• <div class="border3">
    <div class="content">僞類設置的邊框</div>
  </div>

• .border3{  position: relative;}.border3:after{  content: '';  display:block;  position: absolute;  left:0;  top:0;  width: 200%;  height: 200%;  border: 1px solid red;  -webkit-transform-origin: 0 0;  -moz-transform-origin: 0 0;  -ms-transform-origin: 0 0;  -o-transform-origin: 0 0;  transform-origin: 0 0;  -webkit-transform: scale(0.5, 0.5);  -ms-transform: scale(0.5, 0.5);  -o-transform: scale(0.5, 0.5);  transform: scale(0.5, 0.5);  -webkit-box-sizing: border-box;  -moz-box-sizing: border-box;  box-sizing: border-box;}