afert和b的伪类画三角形

/* 提示信息 */
.content-tishi{
    width: 6.93rem;
    margin: 0 auto;
    background: #e9eaea;
    display: flex;
    flex-direction: column;
    margin-top: 0.55rem;
    padding: 0.3rem 0.32rem 0.31rem 0.32rem;
    border-radius: 0.1rem;
    position: relative;
}

.content-tishi::before{
    content: "";
    width: 0.0rem;
    height: 0.2rem;
    display: block;

 三角形重点---------------------------------------
    border-right:0.2rem solid  transparent;
    border-bottom:0.4rem solid #e9eaea;
    border-left: 0.2rem solid transparent;
-------------------------------------------------------------
    position: absolute;
    top: -20px;
    left: 20px;
}