您需要声明<span class="class_name"></span>内的内容。过了它，线就断了。

\A表示换行字符。

.class_name::after {
  content: "\A";
  white-space: pre;
}

使用overflow-wrap: break-word;如:

.yourelement{
  overflow-wrap: break-word;
}

<pre> <---------------------------------------
lorem ipsum
lorem ipsum
lorem ipsum
lorem ipsum
lorem ipsum
</pre> <--------------------------------------

OR

<div style="white-space:pre">  <-----------------------------------
lorem ipsum
lorem ipsum
lorem ipsum
lorem ipsum
lorem ipsum
</div>                         <-----------------------------------

来源:https://stackoverflow.com/a/36191199/2377343

基于之前所说的，这是一个工作的纯CSS解决方案。

<style>
  span {
    display: inline;
  }
  span:before {
    content: "\a ";
    white-space: pre;
  }
</style>
<p>
  First line of text. <span>Next line.</span>
</p>

要使元素在后面有换行符，为它赋值:

显示:块;

块级元素之后的非浮动元素将在下一行出现。许多元素，如<p>和<div>已经是块级元素，所以您可以只使用它们。

But while this is good to know, this really depends more on the context of your content. In your example, you would not want to use CSS to force a line break. The <br /> is appropriate because semantically the p tag is the the most appropriate for the text you are displaying. More markup just to hang CSS off it is unnecessary. Technically it's not exactly a paragraph, but there is no <greeting> tag, so use what you have. Describing your content well with HTMl is way more important - after you have that then figure out how to make it look pretty.

如果这能帮助到某人…

你可以这样做:

<p>This is an <a class="on-new-line">inline link</a>?</p>

用这个css:

a.on-new-line:before { 
  content: ' '; 
  font-size:0; 
  display:block;
  line-height:0;
}