CSS3: How to change style only after manual line break
<p>I try to format a list: The first line should be bold, and the second line should not. But only, if the break is done manually:</p>

<p>HTML</p>

<pre><code>&lt;ul&gt;
&lt;li&gt;This is a long list entry, and the second line should not be formated other than the first line, beacuse this looks stupid&lt;/li&gt;
&lt;li&gt;This is a headline&lt;br /&gt;After the line break, the text should not be bold anymore&lt;/li&gt;
&lt;/ul&gt;
</code></pre>

<p>CSS</p>

<pre><code>li::first-line {
    font-weight: bold;
}
</code></pre>

<p><a href="https://jsfiddle.net/kgf39vwk/" rel="nofollow">https://jsfiddle.net/kgf39vwk/</a></p>

<p>I can`t add more paragraphs or divs or something, because this is content edited by TinyMCE Editor, and it would be much more complex for the user, do do this formatting manually.</p>

<p>Does somebody have an idea?</p>