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<style>

        *{

            margin: 0;

            padding: 0;

        }

        .box{

            width: 100px;

            height: 30px;

            background-color: red;

            text-align: center;

            line-height: 30px;

            margin: 0 auto;

            border: 1px solid black;

            position: relative;

        }

        .box:hover ul{

            display: block;

        }

        ul{

            width: 100px;

            /* display: block; */

            border: 1px solid deeppink;

            left: -1px;

            position: absolute; /*只有当为absolute的时候才能用left:-1px*/

            list-style: none;

            display: none;

        }

 

        li:hover{

            background-color: gray;

        }

    </style>

</head>

<body>

    <div class="box">

        卖家中心

        <ul>

            <li>1</li>

            <li>2</li>

            <li>3</li>

            <li>4</li>

        </ul>

    </div>

</body>

效果图如下:左边为正常是候,右边为hover时候效果

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