article span:first-child {
color: red;
}
---------
<article>
<span>111111111</span> <!-- 红色 -->
<aside>
<span>一一一一一一一一一</span> <!-- 红色 -->
<span>二二二二二二二二二</span>
</aside>
<aside>
<em>haha</em>
<span>oooooooooo</span>
</aside>
</article>
article span:first-of-type {
color: red;
}
----------
<article>
<span>111111111</span> <!-- 红色 -->
<aside>
<span>一一一一一一一一一</span> <!-- 红色 -->
<span>二二二二二二二二二</span>
</aside>
<aside>
<em>haha</em>
<span>oooooooooo</span> <!-- 红色 -->
</aside>
</article>
-
first-child 在同级元素中必须是第一个标签
-
first-of-type 在同级且相同标签中的第一个标签
