css三角

<div class="content-trigon-zhijiao" style="border-width: 0.4rem;">
                                <span class="xian-zi-active">活动<i></i></span>
                            </div>

 .content-trigon-zhijiao{
            width: 0px !important;
            height: 0px!important;
            border-color: rgba(255,0,0,0.5) transparent transparent rgba(255,0,0,0.5);
            border-width: 0.3rem;
            border-style: solid;
            position: absolute;
            top: -0.05rem;
            left: -0.09rem;
        }
        .xian-zi{
            font-size: 0.2rem !important;
            position: absolute;
            bottom: 0;
            right: 0;
            color: #fff !important;
            transform: rotate(-30deg);
        }