margin-top失效, css + div 布局之 CSS盒模型 外边距合并问题_html/css_WEB-ITnose
问题表述：
1 |
|
1 |
|
1 |
|
在经过我用谷歌浏览器的查看DOM 结果后我发现还是因为一些浏览器的代码渲染差别造成的，我就到http://w3school.com.cn/ 上寻求解释。终于在这里
我看出了问题的存在（盒子没有获得 haslayout 造成 margin-top无效），我到百度上又搜索了一下别人是不是也遇到了同样的问题，综合各家说法我最后总结出以下几个问题的重点：
a、全部都为正值，取最大者；
b、不全是正值，则都取绝对值，然后用正值减去最大值；
c、没有正值，则都取绝对值，然后用0减去最大值。
注意：相邻的盒模型可能由DOM元素动态产生并没有相邻或继承关系。 相邻的盒模型中，如果其中的一个是浮动的（floated），垂直margin不会被折叠，甚至一个浮动的盒模型和它的子元素之间也是这样。 设置了overflow属性的元素和它的子元素之间的margin不会被折叠（overflow取值为visible除外）。 设置了绝对定位（position:absolute）的盒模型，垂直margin不会被折叠，甚至和他们的子元素之间也是一样。 设置了display:inline-block的元素，垂直margin不会被折叠，甚至和他们的子元素之间也是一样。 如果一个盒模型的上下margin相邻，这时它的margin可能折叠覆盖（collapse through）它。在这种情况下，元素的位置（position）取决于它的相邻元素的margin是否被折叠。
a、如果元素的margin和它的父元素的margin-top折叠在一起，盒模型border-top的边界定义和它的父元素相同。
b、另外，任意元素的父元素不参与margin的折叠，或者说只有父元素的margin-bottom是参与计算的。如果元素的border-top非零，那么元素的border-top边界位置和原来一样。
一个应用了清除操作的元素的margin-top绝不会和它的块级父元素的margin-bottom折叠。
注意，那些已经被折叠覆盖的元素的位置对其他已经被折叠的元素的位置没有任何影响；只有在对这些元素的子元素定位时，border-top边界位置才是必需的。 根元素的垂直margin不会被折叠。 解决方案：
在父层div加上：overflow:hidden； 把margin-top外边距改成padding-top内边距; 父元素产生边距重叠的边有不为 0 的 padding 或宽度不为 0 且 style 不为 none 的 border
父层div加： padding-top: 1px;
让父元素生成一个 block formating context，以下属性可以实现 * float: left/right * position: absolute * display: inline-block/table-cell(或其他 table 类型) * overflow: hidden/auto 父层div加：position: absolute;
就此截住！
注：本文的总结也是网上其他前辈的辛劳我这里知识借用了一下，在此做出声明：我参考的博文地址有：
http://blog.sina.com.cn/s/blog_6bec36f9010110w9.html
http://hi.baidu.com/jmtbai/blog/item/a91a136ca2d098eb42169456.html
还有一点是我觉得有必要说一下的就是这个效果在IE里面出现在谷歌里面不出现，我找到了一点资料是关于IE浏览器关于渲染的原理：
hasLayout：http://baike.baidu.com/view/2945869.htm
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
Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!
Hot Article
Hot Tools
Notepad++7.3.1
Easy-to-use and free code editor
SublimeText3 Chinese version
Chinese version, very easy to use
Zend Studio 13.0.1
Powerful PHP integrated development environment
Dreamweaver CS6
Visual web development tools
SublimeText3 Mac version
God-level code editing software (SublimeText3)
Hot Topics
1670
14
1428
52
1329
25
1274
29
1256
24
HTML: The Structure, CSS: The Style, JavaScript: The Behavior
Apr 18, 2025 am 12:09 AM
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, CSS, and JavaScript: Web Development Trends
Apr 19, 2025 am 12:02 AM
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 Future of HTML: Evolution and Trends in Web Design
Apr 17, 2025 am 12:12 AM
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.
HTML: Building the Structure of Web Pages
Apr 14, 2025 am 12:14 AM
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 vs. CSS vs. JavaScript: A Comparative Overview
Apr 16, 2025 am 12:04 AM
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.
HTML vs. CSS and JavaScript: Comparing Web Technologies
Apr 23, 2025 am 12:05 AM
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.
HTML: Is It a Programming Language or Something Else?
Apr 15, 2025 am 12:13 AM
HTMLisnotaprogramminglanguage;itisamarkuplanguage.1)HTMLstructuresandformatswebcontentusingtags.2)ItworkswithCSSforstylingandJavaScriptforinteractivity,enhancingwebdevelopment.
What is the difference between <strong>, <b> tags and <em>, <i> tags?
Apr 28, 2025 pm 05:42 PM
The article discusses the differences between HTML tags , , , and , focusing on their semantic vs. presentational uses and their impact on SEO and accessibility.
