CSS伪对象选择符整理

1.E::selection

2.E::placeholder

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1. E::selection

设置对象被选择时的样式。

需要注意的是，::selection只能定义被选择时的background-color，color及text-shadow(IE11尚不支持定义该属性)。

兼容性:

<div class="_selection">
        <p>1. Selecting master branch will publish your site from the master branch. This is useful for repositories dedicated to website content.</p>
        <p>2. Selecting master branch /docs folder will publish from the /docs folder of your master branch. </p>
        <p>3. This lets you maintain documentation and code together on one branch, and open source maintainers can accept contributions for both in a single pull request.</p>
    </div>

._selection p::selection{
    background: #eb4960;
    color: #ffffff;
}

预览： 

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2. E::placeholder

设置对象文字占位符的样式

::placeholder 伪元素用于控制表单输入框占位符的外观，它允许开发者/设计师改变文字占位符的样式，默认的文字占位符为浅灰色。
当表单背景色为类似的颜色时它可能效果并不是很明显，那么就可以使用这个伪元素来改变文字占位符的颜色。
需要注意的是，除了Firefox是 ::[prefix]placeholder，其他浏览器都是使用 ::[prefix]input-placeholder
Firefox支持该伪元素使用text-overflow属性来处理溢出问题。

兼容性：

代码示例

<div class="_placeholder">
        <h1>::placeholder</h1>
        <input type="text" placeholder="::placeholder的演示示例"/>
        <input type="text" placeholder="::placeholder的演示示例"/>
        <input type="text" placeholder="::placeholder的演示示例"/>
        <input type="text" placeholder="::placeholder的演示示例"/>
        <input type="text" placeholder="::placeholder的演示示例"/>
    </div>

._placeholder input {
    width: 400px;
    margin-bottom: 10px;
}
._placeholder input:nth-child(3n)::-webkit-input-placeholder { 
    color: #eb4960;
}
._placeholder input:nth-child(3n):-ms-input-placeholder { /* IE10+ */
    color: #eb4960;
}
._placeholder input:nth-child(3n):-moz-placeholder{  /* Firefox4-18 */
    color: #eb4960;
}
._placeholder input:nth-child(3n)::-moz-placeholder{  /* Firefox19+*/
    color: #eb4960;
}
._placeholder input:nth-child(3n+1)::-webkit-input-placeholder { 
    color: #999999;
}
._placeholder input:nth-child(3n+1):-ms-input-placeholder { /* IE10+ */
    color: #999999;
}
._placeholder input:nth-child(3n+1):-moz-placeholder{  /* Firefox4-18 */
    color: #999999;
}
._placeholder input:nth-child(3n+1)::-moz-placeholder{  /* Firefox19+*/
    color: #999999;
}
._placeholder input:nth-child(3n+2)::-webkit-input-placeholder { 
    color:#008aff;
}
._placeholder input:nth-child(3n+2):-ms-input-placeholder { /* IE10+ */
    color:#008aff;
}
._placeholder input:nth-child(3n+2):-moz-placeholder{  /* Firefox4-18 */
    color:#008aff;
}
._placeholder input:nth-child(3n+2)::-moz-placeholder{  /* Firefox19+*/
    color:#008aff;
}

效果: