How to underline part of a heading (first 40px for instance)?

问题

Is it possible in simple CSS to have a heading underlined partly only, specifically first 50px on the left?

回答1:

You can use the :before pseudo element and add a border to it.

h1 {
  position: relative;
  line-height: 1.2em;
}
h1:before {
  position: absolute;
  left: 0;
  top: 1.2em;
  height: 0;
  width: 50px;
  content: '';
  border-top: 1px solid red;
}

<h1>This is a header, partly underlined</h1>

回答2:

Use a pseudo-element:

h1 {
  position: relative;
}
h1::before {
  content: '';
  position: absolute;
  bottom: 0; left: 0;
  width: 50px;
  height: 2px;
  background-color: green;
}

<h1>foobar</h1>

回答3:

You can add a pseudo element containing a couple of non-breaking spaces that are underlined. This way you get a real underlining instead of a border. However it will still cross over letters like "g".

h1::before {
  content:'\a0\a0\a0\a0\a0\a0\a0\a0';
  display:block;
  position:absolute;
  text-decoration:underline;
  width:50px;
  overflow:hidden;
}

<h1>Headline</h1>
<h1>Another Headline</h1>

来源：https://stackoverflow.com/questions/36860457/how-to-underline-part-of-a-heading-first-40px-for-instance