前面的话
Web早期，HTML是一种很有限的语言，这种语言不关心外观，它只是一种简洁的小型标记机制。随着Mosaic网页浏览器的出现，网站开始到处涌现。对于页面改变外观的需求增加，于是增加了类似和之类的标记元素。几年之后，大多数网站标记几乎完全由表格和font元素组成，且对于所要表现的内容不能传达任何实际含义，使文档可用性降低，且不易于维护。于是1995年，W3C发布了CSS，试图解决结构与样式混杂的问题。
外部样式表
【使用link标记】
在link标记中rel和href属性是必须的，type属性和media属性可省略
<!DOCTYPE html><html lang="en"><head><meta charset="UTF-8"><link rel="stylesheet" href="sheet1.css"><title>Document</title></head><body></body> </html>
body{ background-color: red;} [注意]样式表中不能包含HTML标记语言，只能有CSS规则和CSS注释
/*若CSS文件中存在除了CSS样式和CSS注释的其他标记，则会导致在该标记后面的CSS样式将无法被识别*/<style></style>body{ background-color: red;}
【多个样式表】
一个文档可能关联多个样式表，如果是这样，文档最初显示时只会使用rel为stylesheet的link标记
<!DOCTYPE html><html lang="en"><head><meta charset="UTF-8"><link rel="stylesheet" href="sheet1.css"><link rel="stylesheet" href="sheet2.css"><title>Document</title></head><body></body> </html>
/*sheet1*/body{ background-color: red;}
/*sheet2*/body{ height: 100px; border: 10px solid black;}
【候选样式表】
将rel属性的设置为alternate stylesheet可以定义候选样式表，只有在用户选择这个样式表时才会用于文档表现。如果浏览器能使用候选样式表，它会使用link元素的title属性值生成一个候选样式列表，可在菜单栏中查看->样式中进行选择。(IE和firefox支持)
[注意]若一个候选样式表没有设置title，那么它将无法在候选样式列表中出现，则无法被引用
<!DOCTYPE html><html lang="en"><head><meta charset="UTF-8"><link rel="stylesheet" type="text/css" href="sheet1.css" /><link rel="alternate stylesheet" type="text/css" href="sheet2.css" title="sheet2"/><title>Document</title></head><body></body> </html>
/*sheet1*/body{ background-color: red;}
/*sheet2*/body{ height: 100px; border: 10px solid black;}
内部样式表
【使用style元素】
内部样式表需要使用
<!DOCTYPE html><html lang="en"><head><meta charset="UTF-8"><style>body{ background-color: red;} </style><title>Document</title></head><body></body> </html>
【多个style标签】
文档中可出现多个style标签，且样式规则与层叠样式规则一致
<!DOCTYPE html><html lang="en"><head><meta charset="UTF-8"><style>body{ background-color: red;} </style><style>body{ background-color: blue; height: 100px; border: 10px solid black;} </style><title>Document</title></head><body></body> </html>
【使用@import指令】
与link类似，@import指令用于指示Web浏览器加载一个外部样式表，并在表现HTML文档时使用其样式。唯一的区别在于命令的具体语法和位置。@import指令常用于样式表需要使用另一个样式表中的样式的情况。
<style>@import url(sheet2.css);body{ background-color: red;} </style> [注意]@import必须出现在style元素中，且要放在其他CSS规则之前，否则将根本不起作用。
<!DOCTYPE html><html lang="en"><head><meta charset="UTF-8"><style>/*将@import放置在CSS规则之后将不起使用*/body{ background-color: red;} @import url(sheet2.css);</style><title>Document</title></head><body></body> </html>
【多个@import指令】
可以使用@import指令导入多个CSS样式表，且可以使用media来限制应用场景。
<!DOCTYPE html><html lang="en"><head><meta charset="UTF-8"><style>@import url(sheet1.css) all; @import url(sheet2.css);</style><title>Document</title></head><body></body> </html>
行间样式(内联样式)
如果只是想为单个元素指定一些样式，而不需要嵌套或外部样式表，可以使用HTML的style属性来设置一个行间样式。
<!DOCTYPE html><html lang="en"><head><meta charset="UTF-8"><title>Document</title></head><body style="background-color: red; height: 100px; border: 10px solid black;" style="background-color: red;"></body> </html>
[注意]行间样式若存在多个style属性，只能识别第一个
<!DOCTYPE html><html lang="en"><head><meta charset="UTF-8"><title>Document</title></head><!-- 只能识别第一个style属性的值，所以页面显示为红色--><body style="background-color: red; height: 100px; border: 10px solid black;" style="background-color: blue;"></body> </html>
Beyond HTML: Essential Technologies for Web DevelopmentApr 26, 2025 am 12:04 AMTo build a website with powerful functions and good user experience, HTML alone is not enough. The following technology is also required: JavaScript gives web page dynamic and interactiveness, and real-time changes are achieved by operating DOM. CSS is responsible for the style and layout of the web page to improve aesthetics and user experience. Modern frameworks and libraries such as React, Vue.js and Angular improve development efficiency and code organization structure.
What are boolean attributes in HTML? Give some examples.Apr 25, 2025 am 12:01 AMBoolean 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.
How can you validate your HTML code?Apr 24, 2025 am 12:04 AMHTML 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 vs. CSS and JavaScript: Comparing Web TechnologiesApr 23, 2025 am 12:05 AMHTML, 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.
HTML as a Markup Language: Its Function and PurposeApr 22, 2025 am 12:02 AMThe 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 of HTML, CSS, and JavaScript: Web Development TrendsApr 19, 2025 am 12:02 AMThe 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.
HTML: The Structure, CSS: The Style, JavaScript: The BehaviorApr 18, 2025 am 12:09 AMThe 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: Evolution and Trends in Web DesignApr 17, 2025 am 12:12 AMThe 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.
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