css 样式小窍门

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>页面分布</title>
    <style>
        body {
            margin: 0;  /*让整个页面的边距消失*/
        }
        .pg-head {
            height: 40px;
            background-color: dodgerblue;
            line-height: 30px;   /*调整这个标签里面中的文字水平的位置*/
        }
        .w{
             760px;
            margin:  0 auto; /*居中*/
        }
        ul{
            margin: 0;
            list-style-type: none;
        }
        ul li {
            float: left;
            padding:0 20px 0 20px;
            cursor: pointer;
            margin-top: 4px;
            font-size: 5px;
        }

         ul li:hover{    /*伪类,当鼠标移动当该标签上时自动应用此效果*/
             background-color: darkblue;
         }

    </style>
</head>
<body>
    <div class="pg-head">
        <div class="w">
            <ul>
                <li>菜单一</li>
                <li>菜单二</li>
                <li>菜单三</li>
            </ul>
        </div>
    </div>
    <div class="pg-body"></div>
    <div class="pg-footer"></div>
</body>
</html>