Style is not being applied to H1 element in CSS

问题

I'm facing a strange problem, the style is not being applied to the H1 element.

Code:

p h1 {
  color: red;
}

<p>
  <h1>This is a header</h1>
</p>

回答1:

You can't have a heading (H1 to H6) as a child of a p, that's invalid HTML.

It's not working because your browser is automatically closing the p element before the h1 element starts, leaving you with this generated DOM (code) below:

<p> </p>
<h1>This is a header</h1>
<p> </p>

Using either the F12 to acess your browser's developer tools or using CTRL + U to view the source code, you can see this generated DOM above.

---

Instead, you can have a span inside a p or a heading (H1 to H6)

h1 {
  color: red;
}
h2 span {
  color: green
}
p span {
  color: blue
}

<h1>This is a header</h1>
<h2><span>This</span> is a second header</h2>
<p><span>This</span> is a paragragh</p>

See more about headings contents and phrasing elements in the W3C Specification

来源：https://stackoverflow.com/questions/37838366/style-is-not-being-applied-to-h1-element-in-css