active的英文解释为“积极的”，表现在鼠标上就是点击的意思。关于active选择器最多的示例恐怕就是应用在链接上面的，然而打开链接是一个一瞬间的动作，这不能很好的体现active选择器的特点。
其实我们打开一个带有active链接，激活acive是有一个过程的，就是点击模块后直到松开模块。如果我们不指定这个过程所花费的时间，笔者认为其默认花费零点几秒。
<span style="font-size: 14px"><span style="color: #0000ff"><!</span><span style="color: #ff00ff">DOCTYPE html</span><span style="color: #0000ff">></span>
<span style="color: #0000ff"><</span><span style="color: #800000">html</span><span style="color: #0000ff">></span>
<span style="color: #0000ff"><</span><span style="color: #800000">head</span><span style="color: #0000ff">></span>
<span style="color: #0000ff"><</span><span style="color: #800000">title</span><span style="color: #0000ff">></span>a<span style="color: #0000ff"></</span><span style="color: #800000">title</span><span style="color: #0000ff">></span>
<span style="color: #0000ff"><</span><span style="color: #800000">meta </span><span style="color: #ff0000">name</span><span style="color: #0000ff">="content-type"</span><span style="color: #ff0000"> content</span><span style="color: #0000ff">="text/html; charset=UTF-8"</span><span style="color: #0000ff">></span>
<span style="color: #0000ff"><</span><span style="color: #800000">style</span><span style="color: #0000ff">></span><span style="color: #800000; background-color: #f5f5f5">
a</span><span style="color: #000000; background-color: #f5f5f5">{</span><span style="color: #ff0000; background-color: #f5f5f5">
display</span><span style="color: #000000; background-color: #f5f5f5">:</span><span style="color: #0000ff; background-color: #f5f5f5">block</span><span style="color: #000000; background-color: #f5f5f5">;</span><span style="color: #ff0000; background-color: #f5f5f5">
width</span><span style="color: #000000; background-color: #f5f5f5">:</span><span style="color: #0000ff; background-color: #f5f5f5">30px</span><span style="color: #000000; background-color: #f5f5f5">;</span><span style="color: #ff0000; background-color: #f5f5f5">
margin</span><span style="color: #000000; background-color: #f5f5f5">:</span><span style="color: #0000ff; background-color: #f5f5f5">20px</span><span style="color: #000000; background-color: #f5f5f5">;</span><span style="color: #ff0000; background-color: #f5f5f5">
border-radius</span><span style="color: #000000; background-color: #f5f5f5">:</span><span style="color: #0000ff; background-color: #f5f5f5">8px</span><span style="color: #000000; background-color: #f5f5f5">;</span><span style="color: #ff0000; background-color: #f5f5f5">
padding</span><span style="color: #000000; background-color: #f5f5f5">:</span><span style="color: #0000ff; background-color: #f5f5f5">20px 50px</span><span style="color: #000000; background-color: #f5f5f5">;</span><span style="color: #ff0000; background-color: #f5f5f5">
text-align</span><span style="color: #000000; background-color: #f5f5f5">:</span><span style="color: #0000ff; background-color: #f5f5f5">center</span><span style="color: #000000; background-color: #f5f5f5">;</span><span style="color: #ff0000; background-color: #f5f5f5">
background</span><span style="color: #000000; background-color: #f5f5f5">:</span><span style="color: #0000ff; background-color: #f5f5f5">green</span><span style="color: #000000; background-color: #f5f5f5">;</span>
<span style="color: #000000; background-color: #f5f5f5">}</span><span style="color: #800000; background-color: #f5f5f5">
a:active</span><span style="color: #000000; background-color: #f5f5f5">{</span><span style="color: #ff0000; background-color: #f5f5f5">
background</span><span style="color: #000000; background-color: #f5f5f5">:</span><span style="color: #0000ff; background-color: #f5f5f5">indigo</span><span style="color: #000000; background-color: #f5f5f5">;</span>
<span style="color: #000000; background-color: #f5f5f5">}</span>
<span style="color: #0000ff"></</span><span style="color: #800000">style</span><span style="color: #0000ff">></span>
<span style="color: #0000ff"></</span><span style="color: #800000">head</span><span style="color: #0000ff">></span>
<span style="color: #0000ff"><</span><span style="color: #800000">body</span><span style="color: #0000ff">></span>
<span style="color: #0000ff"><</span><span style="color: #800000">a </span><span style="color: #ff0000">href</span><span style="color: #0000ff">="paris.jpg"</span><span style="color: #0000ff">></span>link<span style="color: #0000ff"></</span><span style="color: #800000">a</span><span style="color: #0000ff">></span>
<span style="color: #0000ff"></</span><span style="color: #800000">body</span><span style="color: #0000ff">></span>
<span style="color: #0000ff"></</span><span style="color: #800000">html</span><span style="color: #0000ff">></span></span>
我们可以通过过渡属性（transition）来调整这个时间。
<span style="color: #000000; font-size: 14px"> a:active{
background:indigo;
transition:3s;
}</span>
读者可以做一个实验，改变其中transition的值，然后测试:avtive选择器所花费的时间。
<span style="font-size: 14px"><span style="color: #0000ff"><!</span><span style="color: #ff00ff">DOCTYPE html</span><span style="color: #0000ff">></span>
<span style="color: #0000ff"><</span><span style="color: #800000">html</span><span style="color: #0000ff">></span>
<span style="color: #0000ff"><</span><span style="color: #800000">head</span><span style="color: #0000ff">></span>
<span style="color: #0000ff"><</span><span style="color: #800000">title</span><span style="color: #0000ff">></span>a<span style="color: #0000ff"></</span><span style="color: #800000">title</span><span style="color: #0000ff">></span>
<span style="color: #0000ff"><</span><span style="color: #800000">meta </span><span style="color: #ff0000">name</span><span style="color: #0000ff">="content-type"</span><span style="color: #ff0000"> content</span><span style="color: #0000ff">="text/html; charset=UTF-8"</span><span style="color: #0000ff">></span>
<span style="color: #0000ff"><</span><span style="color: #800000">style</span><span style="color: #0000ff">></span><span style="color: #800000; background-color: #f5f5f5">
div
</span><span style="color: #000000; background-color: #f5f5f5">{</span><span style="color: #ff0000; background-color: #f5f5f5">
width</span><span style="color: #000000; background-color: #f5f5f5">:</span><span style="color: #0000ff; background-color: #f5f5f5">100px</span><span style="color: #000000; background-color: #f5f5f5">;</span><span style="color: #ff0000; background-color: #f5f5f5">
height</span><span style="color: #000000; background-color: #f5f5f5">:</span><span style="color: #0000ff; background-color: #f5f5f5">100px</span><span style="color: #000000; background-color: #f5f5f5">;</span><span style="color: #ff0000; background-color: #f5f5f5">
background</span><span style="color: #000000; background-color: #f5f5f5">:</span><span style="color: #0000ff; background-color: #f5f5f5">red</span><span style="color: #000000; background-color: #f5f5f5">;</span><span style="color: #ff0000; background-color: #f5f5f5">
transition</span><span style="color: #000000; background-color: #f5f5f5">:</span><span style="color: #0000ff; background-color: #f5f5f5"> 5s</span><span style="color: #000000; background-color: #f5f5f5">;</span>
<span style="color: #000000; background-color: #f5f5f5">}</span><span style="color: #800000; background-color: #f5f5f5">
div:active
</span><span style="color: #000000; background-color: #f5f5f5">{</span><span style="color: #ff0000; background-color: #f5f5f5">
width</span><span style="color: #000000; background-color: #f5f5f5">:</span><span style="color: #0000ff; background-color: #f5f5f5">300px</span><span style="color: #000000; background-color: #f5f5f5">;</span><span style="color: #ff0000; background-color: #f5f5f5">
height</span><span style="color: #000000; background-color: #f5f5f5">:</span><span style="color: #0000ff; background-color: #f5f5f5">300px</span><span style="color: #000000; background-color: #f5f5f5">;</span><span style="color: #ff0000; background-color: #f5f5f5">
transition</span><span style="color: #000000; background-color: #f5f5f5">:</span><span style="color: #0000ff; background-color: #f5f5f5">3s</span><span style="color: #000000; background-color: #f5f5f5">;</span>
<span style="color: #000000; background-color: #f5f5f5">}</span>
<span style="color: #0000ff"></</span><span style="color: #800000">style</span><span style="color: #0000ff">></span>
<span style="color: #0000ff"></</span><span style="color: #800000">head</span><span style="color: #0000ff">></span>
<span style="color: #0000ff"><</span><span style="color: #800000">body</span><span style="color: #0000ff">></span>
<span style="color: #0000ff"><</span><span style="color: #800000">div</span><span style="color: #0000ff">></</span><span style="color: #800000">div</span><span style="color: #0000ff">></span>
<span style="color: #0000ff"></</span><span style="color: #800000">body</span><span style="color: #0000ff">></span>
<span style="color: #0000ff"></</span><span style="color: #800000">html</span><span style="color: #0000ff">></span>
</span>这里面有两个transition，也就是意味着有两个过渡。
如果读者只设置了在 div 里面的 transition ，那么选择器的过渡时间也就默认为 div 里的 transition 了。
如果读者有兴趣也可以试一试transition和其他选择器的组合。
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