因为我没有声誉来评论，我将在这里给出一些想法。

如果你想要一个可变高度的CSS，去掉所有的边框，并给出一个背景色。

    hr{
        height:2px;
        border:0px;
        background:green;
        margin:0px;/*sometimes useful*/
    }
    /*Doesn't work in ie7 and below and in Quirks Mode*/

if you want simply a style that you know that will work (example: to replace a border in a ::before element for most email clients or hr{ height:0px; border:0px; border-top:2px solid blue; margin:0px;/*useful sometimes*/ } In both ways, if you set a width, it will always have it's size. No need to set display:block; for this. To be totally safe, you can mix both, 'cause some browsers can get confused with height:0px;: hr{ height:1px; border:0px; background:blue; border-top:1px solid blue; margin:0px;/*useful sometimes*/ } With this method you can be sure that it will have at least 2px in height. It's a line more, but safety is safety. This is the method you should use to be compatible with almost everything. Remember: Gmail only detects inline css and some email clients may not support backgrounds or borders. If one fails, you will still have a 1px line. Better than nothing. In the worst cases, you can try to add color:blue;. In the worst of the worst cases, you can try to use a <font color="blue"></font> tag and put your precious <hr/> tag inside it. It will inherit the <font></font> tag color. With this method, you WILL want to do like this: <hr width="50" align="left"/>. Example: <span> awhieugfrafgtgtfhjjygfjyjg <font color="#42B3E5"><hr width="50" align="left"/></font> </span> <!--Doesn't work in ie7 and below and in Quirks Mode--> Here is a link for you to check: http://jsfiddle.net/sna2D/

在阅读了这里所有的答案，并看到了所描述的复杂性之后，我开始了一个关于人力资源实验的小转移。并且，结论是你可以扔掉你写的大部分monkeypatched CSS，阅读这篇小入门，只使用这两行纯CSS:

hr {
  border-style: solid;
  border-color: cornflowerblue; /* or whatever */
}

这就是你为人事简历设计风格所需要的全部内容。

适用于跨浏览器、跨设备、跨操作系统、跨英语频道、跨年龄。 没有“我认为这可以工作……”，“你需要记住Safari/IE……”等等。 没有额外的CSS -没有高度，宽度，背景颜色，颜色等涉及。

只有防弹的彩色hr。就是这么简单。

奖励:给HR一些高度H，只要设置边界宽度为H/2。

你应该设置border-width为0;它在火狐和Chrome浏览器上运行良好。

人力资源{ 明确:; 颜色:红色; 背景颜色:红色; 身高:1 px; 边框宽度:0; ｝ <人力资源/ > 这是一个测试 <人力资源/ >

它很简单，也是我的最爱。

<hr style="background-color: #dd3333" />

我喜欢设置边界顶部的答案，但他们不知何故仍然有点离开Chrome… 但是如果我设置border-top: 1px纯黑色;And border-bottom: 0px;我最终得到了一条真正的单线(这也适用于更高的厚度)。

我认为这是最有效的方法:

<hr style="border-top: 1px solid #ccc; background: transparent;">

或者如果你喜欢在所有的hr元素上写这个CSS:

hr {
  background-color: transparent;
  border-top: 1px solid #ccc;
}