给块级元素绘制0.5px边框

.con {
        position: relative;
    }
    .con::after {
        position: absolute;
        bottom: 0;
        left: 0;
        z-index: 1;
        width: 200%;
        height: 200%;
        content: "";
        display: block;
        border: 1px solid #FF2831;
        transform: scale(0.5);
        transform-origin: left bottom;
    }