.welcome-hero{    display: flex;    align-items: center;    justify-content: center;    position:relative;    background:url(../images/about/welcome-banner.jpg)no-repeat;#图片    background-size:cover;    background-position: center;    height:890px;}.welcome-hero:before{    position:absolute;    content: " ";    top:0;    left:0;    background:rgba(31,44,108,.65);#添加上去的颜色    width:100%;    height:100%;}