两种常见伪类和盒模型常用属性

两种伪类实例：

1.位置伪类：

/* 为所有的列表设置虚线边框，顺带复习了一下选择器权重 */
.list > li:nth-of-type(n) {
    border: 1px dashed gray;
}
.item {
    border: 1px solid lightblue;
}
/* 头两行设置背景色 */
.list > li:nth-of-type(-n+2){
    background-color: aqua;
}
/* 最后两行设置背景色 */
.list > li:nth-last-of-type(-n+2){
    background-color:chartreuse;
}
/* 第一行 */
.list > li:first-of-type{
    background-color: blue;
    font-weight: 800;
    color:aliceblue;
}
/* 最后一行 */
.list > li:last-of-type{
    background-color: brown;
    font-weight: 900;
    color:white;
}
/* 设置偶数行，也可以用2n */
.list > li:nth-of-type(even){
    border: 1px dashed gray;
}
/* 设置奇数行 也可以用2n+1或2n-1*/
.list > li:nth-of-type(odd){
    border: 1px dashed gray;  
}
/* 任意设置行 */
.list > li:nth-of-type(n+3){
    border: 1px dashed gray;
}

<!DOCTYPE html>
<html lang="zh-CN">
<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>位置伪类</title>
    <link rel="stylesheet" href="css/demo2.css">
</head>
<body>
    <ul class="list">
        <li class="item">item1</li>
        <li class="item">item2</li>
        <li class="item">item3</li>
        <li class="item">item4</li>
        <li class="item">item5</li>
        <li class="item">item6</li>
        <li class="item">item7</li>
        <li class="item">item8</li>
    </ul>
</body>
</html>

2.状态伪类：

legend{
    text-align: center;
    border: 1px solid cyan;
}
/* 状态伪类 */
input:focus{
    background-color: burlywood;
}
input:checked + label{
   color: cyan;
   font-weight: bolder;
}
button{
    height: 30px;
    background-color: coral;
    outline: none;
    border: none;
    border-radius: 2px;
    color:aliceblue
}
/* 状态伪类 */
button:hover{
    cursor: pointer;
    background-color: aqua;
    color:coral;
}

<!DOCTYPE html>
<html lang="zh-CN">
<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>伪类</title>
    <link rel="stylesheet" href="css/demo1.css">
</head>
<body>
    <form action="" method="get">
        <fieldset>
            <legend>用户注册列表</legend>
            <br />
            <label for="username">用户名：</label>
            <input type="text" name="username" id="username">
            <br />
            <label for="psd">密码：<input type="password" name="password" id="psd"> </label>
            <br />
            <label for="m">性别：</label>
            <input type="radio" name="sex" id="m" value="男" checked><label for="m">男</label>
            <input type="radio" name="sex" id="f" value="女" ><label for="f">女</label>
            <input type="radio" name="sex" id="s" value="保密"><label for="s">保密</label>
            <br/>
            <label for="swing">特长：</label>
            <input type="checkbox" name="fa" id="swing" value="游泳" ><label for="swing">游泳</label>
            <input type="checkbox" name="fa" id="drive" value="骑马" ><label for="drive">骑马</label>
            <input type="checkbox" name="fa" id="shejian" value="射箭" checked><label for="shejian">射箭</label>
            <input type="checkbox" name="fa" id="pandeng" value="攀登" ><label for="pandeng">攀登</label>
            <br/>
            <button>提交</button>
        </fieldset>
    </form>
</body>
</html>

盒模型及常用属性示例

.box{
    width:500px;
    height:300px;
    border:2px dashed coral;
    padding:10px 20px;
    margin:15px 10px 20px 10px;
    text-align: center;
}
.hello{
    width:200px;
    height:200px;
    float: left;
    border:2px dashed cyan;
    padding:0;
    margin:0;
    text-align: left;
}
.hello1{
    width:200px;
    height:200px;
    float: right;
    border:2px dashed cyan;
    padding:0;
    margin:0;
    text-align: right;
    box-sizing: border-box;
}

<!DOCTYPE html>
<html lang="zh-CN">
<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>盒模型及常用属性</title>
    <link rel="stylesheet" href="css/demo3.css">
</head>
<body>
    <div class="box">
        <p>随便写几个字示意示意</p> 
        <div class="hello">
            这里边再放一个盒子呢？
        </div>
        <div class="hello1">
            右边来一个？
        </div>
    </div>
</body>
</html>