0.5px的线

div{
width：100px;
height:100px;
position: relative;
     &::before{
            display: block;
             100%;
            content: '';
            height:1px;
            background-color: rgba(52,56,75, 0.1);
            position: absolute;
            left: 0;
            bottom: 0;
            transform: scaleY(.5);
    }   
}