外边距合并
当两个垂直方向外边距相遇,它们将形成一个折叠外边距。
合并后的外边距的高度等于两个发生合并的外边距的高度中的较大者。
为了好认识,我们称内部div为"盒子",包含这个内部div的外部div为"包含体"
解释
- 盒子margintop和包含体margintop取出最终折叠外边距值。下面为取这个值的情况 150 50=150 150 -50=100 -150 -50 =-150 -150 50 =-100
- 两个相邻的外边距都是正数时,折叠结果是它们两者之间较大的值。可以在下面例子2中,改变一下
- 两个相邻的外边距都是负数时,折叠结果是两者绝对值的较大值。
- 两个外边距一正一负时,折叠结果是两者的相加的和。
- 包含关系时,盒子不显示margin-top(相当没有margin-top),包含体显示margin-top这个最终值。
- 兄弟关系时,两兄弟之间的margin共用这个最终值。
极限情况一个元素
例子1包含关系,不设置外层div的内边距(补白)和边框的前提!
<meta charset="utf-8"><style type="text/css"> * {margin:0;padding:0;border:0;} #outer {width:200px;height:200px;background-color:red;margin-top:-20px;} #inner {width:50px;height:50px;background-color:blue;margin-top:50px;}</style>
<div id="outer"> <div id="inner"> </div></div><!--不设置 div 的内边距和边框,那么内部 div 的上外边距将与外部 div 的上外边距合并(叠加),内部div箱单更木有margin-top。外部用这个最大值。-->
例子2兄弟关系
* {margin:0; padding:0;border:0;}#d1 {width:100px;height:100px;margin-top:50px;margin-bottom:50px;background-color:red;}/*改变margin-bottom:-50px;试一试*/#d2 {width:100px;height:100px;margin-top:10px;background-color:blue;}
<div id="d1"></div><div id="d2"></div><!--两个 div 之间的外边距是 50px,并不是 60px(50px + 10px)。-->
例子3本身合并``它有外边距,但是没有边框或填充。在这种情况下,上外边距与下外边距就碰到了一起,它们会发生合并:
* {margin:0; padding:0;border:0;}#d1{border: 1px solid red;width: 200px;}#d2 {height:0px;min-height:0px;margin-top:50px;margin-bottom:150px;}/*border: 1px solid red;试一试将这个盒子边框加上,是不是还能合并。答案不能!*/
<div id="d1"> <div id="d2"></div></div>
从图中可以看到这个红色边框包裹的高度是150px,不是200px。包含体本身木有高度,随着盒子的最后得到的折叠margin自动撑开。
例子3调试注意
但是在浏览器调试的时候,监视盒子的时候,并不是给我们显示折叠margin值。而是显示这个盒子的设定值。这点不要影响,最终的折叠margin值的肯定。
例子3Question!!求答案,想了一下午。
减轻上面的影响请试一试一下代码
* {margin:0; padding:0;border:0;}#d2 {height:0px;min-height:0px;margin-top:50px;margin-bottom:150px;}<div id="d2"></div>
从上面注意我们知道:调试的时候选中这个元素,显示200px是正常的,但是这个元素距离浏览器上面100px,这个我真不能理解。
不能产生折叠边距的情况

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.

HTMLisnotaprogramminglanguage;itisamarkuplanguage.1)HTMLstructuresandformatswebcontentusingtags.2)ItworkswithCSSforstylingandJavaScriptforinteractivity,enhancingwebdevelopment.

HTML is the cornerstone of building web page structure. 1. HTML defines the content structure and semantics, and uses, etc. tags. 2. Provide semantic markers, such as, etc., to improve SEO effect. 3. To realize user interaction through tags, pay attention to form verification. 4. Use advanced elements such as, combined with JavaScript to achieve dynamic effects. 5. Common errors include unclosed labels and unquoted attribute values, and verification tools are required. 6. Optimization strategies include reducing HTTP requests, compressing HTML, using semantic tags, etc.

HTML is a language used to build web pages, defining web page structure and content through tags and attributes. 1) HTML organizes document structure through tags, such as,. 2) The browser parses HTML to build the DOM and renders the web page. 3) New features of HTML5, such as, enhance multimedia functions. 4) Common errors include unclosed labels and unquoted attribute values. 5) Optimization suggestions include using semantic tags and reducing file size.

WebdevelopmentreliesonHTML,CSS,andJavaScript:1)HTMLstructurescontent,2)CSSstylesit,and3)JavaScriptaddsinteractivity,formingthebasisofmodernwebexperiences.


Hot AI Tools

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Undress AI Tool
Undress images for free

Clothoff.io
AI clothes remover

AI Hentai Generator
Generate AI Hentai for free.

Hot Article

Hot Tools

SecLists
SecLists is the ultimate security tester's companion. It is a collection of various types of lists that are frequently used during security assessments, all in one place. SecLists helps make security testing more efficient and productive by conveniently providing all the lists a security tester might need. List types include usernames, passwords, URLs, fuzzing payloads, sensitive data patterns, web shells, and more. The tester can simply pull this repository onto a new test machine and he will have access to every type of list he needs.

WebStorm Mac version
Useful JavaScript development tools

ZendStudio 13.5.1 Mac
Powerful PHP integrated development environment

Safe Exam Browser
Safe Exam Browser is a secure browser environment for taking online exams securely. This software turns any computer into a secure workstation. It controls access to any utility and prevents students from using unauthorized resources.

MinGW - Minimalist GNU for Windows
This project is in the process of being migrated to osdn.net/projects/mingw, you can continue to follow us there. MinGW: A native Windows port of the GNU Compiler Collection (GCC), freely distributable import libraries and header files for building native Windows applications; includes extensions to the MSVC runtime to support C99 functionality. All MinGW software can run on 64-bit Windows platforms.