我是用sass寫的，用其他的前處理器寫法大同小異，新建mixin.scss檔案：

/*單條border樣式*/
@mixin border-1px ($color, $direction) {
  content: '';
  position: absolute;
  background: $color;
  @if $direction == left {
    left: 0;
    top: 0;
    height: 100%;
    width: 2px;
    transform: scaleX(0.5);
    transform-origin: left 0;
  }
  @if
 
 $direction == right {
    right: 0;
    top: 0;
    height: 100%;
    width: 2px;
    transform: scaleX(0.5);
    transform-origin: right 0;
  }
  @if $direction == bottom {
    bottom: 0;
    left: 0;
    width: 100%;
    height: 2px;
    transform: scaleY(0.5);
    transform-origin: 0 bottom;
  }
  @if $direction == top
 
 {
    top: 0;
    left: 0;
    width: 100%;
    height: 2px;
    transform: scaleY(0.5);
    transform-origin: 0 top;
  }
}

/*四條border樣式*/
@mixin all-border-1px ($color, $radius) {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  border: 2px solid $color;
  border-radius: $radius * 2;
  -webkit-box-sizing
 
: border-box;
  box-sizing: border-box;
  width: 200%;
  height: 200%;
  -webkit-transform: scale(0.5);
  transform: scale(0.5);
  -webkit-transform-origin: left top;
  transform-origin: left top;
}

然後在需要的地方@include匯入就行。