前端问题：伪类first-child 有时候不起作用
<style>
article:first-child {
color: red;//不生效
}
</style>
<h1>logo</h1>
<article>article1</article>
<article>article2</article>
<article>article3</article>
改进：
<style>
article:first-child {
color: red;//不生效
}
</style>
<h1>logo</h1>
<div>
<article>article1</article>
<article>article2</article>
<article>article3</article>
</div>