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:
暂时也就整理这么多吧!后续再补充....

Boolean attributes are special attributes in HTML that are activated without a value. 1. The Boolean attribute controls the behavior of the element by whether it exists or not, such as disabled disable the input box. 2.Their working principle is to change element behavior according to the existence of attributes when the browser parses. 3. The basic usage is to directly add attributes, and the advanced usage can be dynamically controlled through JavaScript. 4. Common mistakes are mistakenly thinking that values need to be set, and the correct writing method should be concise. 5. The best practice is to keep the code concise and use Boolean properties reasonably to optimize web page performance and user experience.

HTML code can be cleaner with online validators, integrated tools and automated processes. 1) Use W3CMarkupValidationService to verify HTML code online. 2) Install and configure HTMLHint extension in VisualStudioCode for real-time verification. 3) Use HTMLTidy to automatically verify and clean HTML files in the construction process.

HTML, CSS and JavaScript are the core technologies for building modern web pages: 1. HTML defines the web page structure, 2. CSS is responsible for the appearance of the web page, 3. JavaScript provides web page dynamics and interactivity, and they work together to create a website with a good user experience.

The function of HTML is to define the structure and content of a web page, and its purpose is to provide a standardized way to display information. 1) HTML organizes various parts of the web page through tags and attributes, such as titles and paragraphs. 2) It supports the separation of content and performance and improves maintenance efficiency. 3) HTML is extensible, allowing custom tags to enhance SEO.

The future trends of HTML are semantics and web components, the future trends of CSS are CSS-in-JS and CSSHoudini, and the future trends of JavaScript are WebAssembly and Serverless. 1. HTML semantics improve accessibility and SEO effects, and Web components improve development efficiency, but attention should be paid to browser compatibility. 2. CSS-in-JS enhances style management flexibility but may increase file size. CSSHoudini allows direct operation of CSS rendering. 3.WebAssembly optimizes browser application performance but has a steep learning curve, and Serverless simplifies development but requires optimization of cold start problems.

The roles of HTML, CSS and JavaScript in web development are: 1. HTML defines the web page structure, 2. CSS controls the web page style, and 3. JavaScript adds dynamic behavior. Together, they build the framework, aesthetics and interactivity of modern websites.

The future of HTML is full of infinite possibilities. 1) New features and standards will include more semantic tags and the popularity of WebComponents. 2) The web design trend will continue to develop towards responsive and accessible design. 3) Performance optimization will improve the user experience through responsive image loading and lazy loading technologies.

The roles of HTML, CSS and JavaScript in web development are: HTML is responsible for content structure, CSS is responsible for style, and JavaScript is responsible for dynamic behavior. 1. HTML defines the web page structure and content through tags to ensure semantics. 2. CSS controls the web page style through selectors and attributes to make it beautiful and easy to read. 3. JavaScript controls web page behavior through scripts to achieve dynamic and interactive functions.


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