CSS文件中定义常量

 $sliderIndex : 100;

.sliderShowing{
    animation: openAnim 0.5s linear;
    width: $leftAreaWidth;
    height: 100%;
    background-color: transparent;
    display: flex;
    position: relative;
    z-index: $sliderIndex;
}

.sliderHiden{
    width: $tabWidth;
    height: 100%;
    background-color: transparent;
    display: flex;
    position: absolute;
    z-index: $sliderIndex;
}