:root
        {
            --nav-link-height: 36px;}
        .header-img-warpper {
            background-image: linear-gradient(45deg, firebrick, indianred);}

        .header-img {
            background-image: url(https://stu.henu.edu.cn/images/stu-logo.png);
            height: 90px;
            background-size: contain;
            background-repeat: no-repeat;
            background-position-y: center;
            background-position-x: left;
            position: relative;}