css 定位

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>定位</title>
    <style>
        * {
            margin: 0;
            padding: 0;
            box-sizing: border-box;
        }

        li {
            list-style-type: none;
        }

        a {
            text-decoration: none;
            color: rgb(82, 79, 79);
        }

        .nav {
            height: 50px;
            border: 1px solid #ccc;
            margin-top: 5px;
        }

        .nav li {
            /* height: 48px; */
            float: left;
            width: 20%;
            border-right: 1px solid #ccc;
        }

        .nav li a {
            display: block;
            height: 48px;
            text-align: center;
            line-height: 48px;
            position: relative;
        }

        .nav li a .code {
            position: absolute;
            /* 从水平距离一半的位置开始，图片水平并不是居中显示 */
            left: 50%;
            /* 垂直距离 距离顶部50px */
            top: 50px;
            /* 图片水平位置居中显示，减掉图片一半的宽度 */
            transform: translate(-50%);
            display: none;
        }
    </style>
</head>

<body>
    <script>
        function over() {
            var code = document.getElementsByClassName("code");
            var len = code.length;
            code[len - 1].style.display = "block";
        }
        function out() {
            var code = document.getElementsByClassName("code");
            code[0].style.display = "none"
        }
    </script>

    <div class="nav">
        <ul>
            <li onmouseover="over()" onmouseout="out()">
                <a href="#">
                    导航显示
                    <img src="./html+css/study/code.png" alt="" class="code">
                </a>
            </li>
            <li><a href="#">导航显示</a></li>
            <li><a href="#">导航显示</a></li>
            <li><a href="#">导航显示</a></li>
            <li><a href="#">导航显示</a></li>
        </ul>
    </div>
</body>

</html>