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HomeWeb Front-endHTML TutorialCSS 之 选择器_html/css_WEB-ITnose

选择器

类型选择器

也叫做 元素选择器和简单选择器,可以根据元素标签指定样式。

p {color:red;}

类选择器

一般用于某些同类型的样式。

.xxxClass{}<div class="xxxClass"></div>

ID选择器

为特殊的元素,指定类型

#xxxId{}<div id="xxxId"></div>

后代选择器

在某个选择器后,选择指定规则的后代,为其指定样式

div p {}

伪类选择器

为某些特殊的元素,在某些条件时,指定样式。
比如,链接的link和visited ;
以及其他元素的hover,focus,active等。

a:link, a:visited {}a:hover, a:focus, a:active {}

通用选择器

类似通配符的作用,比如所有可用元素添加样式。

*{}

高级选择器

子选择器

后代选择器是选择所有的后代,子选择器则可以选择元素的直接后代,即子元素。

#nav>li{}

相邻选择器

#nav + p {}

属性选择器

比如为tooltip添加样式

acronym[title]{}

样式层叠

由于选择同一个元素可以通过不同的方法,比如元素的后代、或者类、或者ID,那么就可能造成样式的重叠。因此可以使用!important,增加样式的优先级。

样式特殊性

再说到样式的重叠的另一种情况,如果不同的方式都指定了样式,到底会优先使用哪一种呢?
这就需要了解特殊性了,从上到下 依次为:

#xxx{}.class{}body div{}div{}

即,元素上的style会优先、其次是使用ID选择器、然后是类选择器、后代选择器、最后是类型选择器

样式的继承

样式是可以继承的,比如给body增加样式,那么页面中body内的所有元素都会应用这个样式。

样式的引用

样式的引用由两种方式,一种是通过链接link,另一种则是style的导入的方式:

    <!-- <link rel="stylesheet" type="text/css" href="test.css"> -->    <style type="text/css">    /*slow*/    @import url("test.css");    </style>

相比较来说,link的方式要更快一些。

另外,还是推荐把CSS都放在同一个文件中。因为浏览器加载样式文件,是受浏览器的限制的,有的浏览器只支持同时下载3个文件、有的支持8个...
如果由三个文件,而浏览器只能同时下载2个文件,那么第三个就必须要等到前两个下载完后,才能加载。
因此,放在一个文件中会更快的加载。

如果把所有的CSS都放在一个文件,又可能导致文件过于庞大,不易维护。因此有以下几个建议:

  • 完善注释信息
  • 对样式进行分组,并写入相应的注释,可以加快定位
  • 发布时,可以考虑对文件进行压缩,比如删除注释、删除空白、压缩。目前很多的浏览器都支持从压缩包中下载文件,这样可以有效的减少文件体积。
  • 暂时也就整理这么多吧!后续再补充....

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