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：
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: