f="fonts.html#propdef-font-size" class="noxref"><span class="propinst-font-size">'font-size'</span></a></li>
<li><strong>ex</strong>：相关字体的<span class="descinst">'x-height'</span></li>

</ul>

<div class="example"><P style="display:none">示例：</P>
<pre><code class="css">
h1 { margin: 0.5em }      /* em */
h1 { margin: 1ex }        /* ex */
</code></pre>
</div>

<p><span class="index-def" title="em (unit)|quad width"><a
name="em-width">'em'</a></span>单位等于应用该规则的元素的<a h