SOURCE

<p>
  我是字
  <em>
    我是斜体字
  </em>
  我是字
</p>
<br />
<p>
  我是字
  <em style="vertical-align:40px;line-height:80px">
    我是斜体字
  </em>
  我是字
</p>
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<p class="p1">
  我有字体没行高
</p>
<br />
<br />
<p class="p2">
  我有行高没字体
</p>
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<span class="s1">
  abc
</span>
<span class="s2">
  abc
</span>
<span class="s3">
  abc
</span>
<div class="s3">
  <span class="s4">
    abc
  </span>
</div>

* {
  margin:0;
  padding:0;
}

p {
  background-color: lightgray;
}

.p1 {
  line-height: 0;
  font-size: 50px;
}

.s1 {
  font-size: 50px;
  line-height: 100px;
  background: blue;
}

.s2 {
  font-size: 50px;
  line-height: 100px;
  display: inline-block;
  background: red;
}

.s3 {
  font-size: 50px;
  line-height: 100px;
  background: green;
  font-family: 'simsun';
}

.s4 {
  font-size: 50px;
  line-height: 100px;
  background: purple;
  font-family: 'simsun';
}

.p2 {
  line-height: 50px;
  font-size: 0px;
}