div居中的问题_html/css_WEB-ITnose
div {
margin: auto;
position: absolute;
top: 0;
left: 0;
right: 0
bottom: 0;
width: 100px;
height: 100px;
border:1px solid red;
}
将产生一个div， width: 100px; height: 100px; 外边框 1px 红色实线 ；
div居于屏幕中间，对于居于中间这点，我无法理解,为何下面的做法不可以？
div {
margin: auto;
position: absolute;
top: 0;
left: 0;
width: 100px;
height: 100px;
border:1px solid red;
}
回复讨论(解决方案)
问题1
top: 0;
left: 0;
为何不可以代替
top: 0;
left: 0;
right: 0
bottom: 0;
问题2
margin:auto为何不可以代替
margin: auto;
top: 0;
left: 0;
right: 0
bottom: 0;
<html> <head> <style type="text/css"> div { margin: auto; position: absolute; right: 0; bottom: 0; top: 0; left: 0; width: 100px; height: 100px; border:1px solid red; } </style> </head> <body> <div></div> </body></html>打开浏览器，改变浏览器的视区的大小，发现依然居中
因为该div设置了position为absolute，而且设置了置入值（left\right\top\bottom），根据元素包含块的定义，因为div的父级没有position为“absolute”、“relative”或者“fixed”的祖先元素，所以该div的包含块为初始包含块，即根元素html的包含块，我在控制台选中html标签的时候，可以看出整个视区都被选中，所以这个时候初始包含块就是视区
根据css2.1中‘top’ + ‘margin-top’ + ‘border-top-width’ + ‘padding-top’ + ‘height’ + ‘padding-bottom’ + ‘border-bottom-width’ + ‘margin-bottom’ + ‘bottom’ = 包含块的高度
设置margin的属性为auto恰好填充了空白
可以在控制台看出随着视区大小变化，margin的值随之变化
问题1：
如果只有left属性和top属性 那么margin属性为auto没有起到任何的作用
只有设置了left和right，或者top与bottom的时候，margin为auto的时候才会去填充左右或者上下的空白，达到left属性0，right属性为0，top属性为0，bottom属性为0 的效果，不然div只有100*100那么大，不可能达到left为0又right为0的效果啊！只有添加margin，增大在文档流的占用空间
问题2：
同理问题1，不设置置入值（left\right\top\bottom），这个时候margin属性为auto没有起到任何的作用
<html> <head> <style type="text/css"> div { margin: auto; position: absolute; right: 0; bottom: 0; top: 0; left: 0; width: 100px; height: 100px; border:1px solid red; } </style> </head> <body> <div></div> </body></html>打开浏览器，改变浏览器的视区的大小，发现依然居中
因为该div设置了position为absolute，而且设置了置入值（left\right\top\bottom），根据元素包含块的定义，因为div的父级没有position为“absolute”、“relative”或者“fixed”的祖先元素，所以该div的包含块为初始包含块，即根元素html的包含块，我在控制台选中html标签的时候，可以看出整个视区都被选中，所以这个时候初始包含块就是视区
根据css2.1中‘top’ + ‘margin-top’ + ‘border-top-width’ + ‘padding-top’ + ‘height’ + ‘padding-bottom’ + ‘border-bottom-width’ + ‘margin-bottom’ + ‘bottom’ = 包含块的高度
设置margin的属性为auto恰好填充了空白
可以在控制台看出随着视区大小变化，margin的值随之变化
问题1：
如果只有left属性和top属性 那么margin属性为auto没有起到任何的作用
只有设置了left和right，或者top与bottom的时候，margin为auto的时候才会去填充左右或者上下的空白，达到left属性0，right属性为0，top属性为0，bottom属性为0 的效果，不然div只有100*100那么大，不可能达到left为0又right为0的效果啊！只有添加margin，增大在文档流的占用空间
问题2：
同理问题1，不设置置入值（left\right\top\bottom），这个时候margin属性为auto没有起到任何的作用
上面描述增大在文档流的占用空间不正确，position属性为absolute已经脱离了文档流，应该是增大该div的占用空间比较准确一点
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
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
Difficulty in updating caching of official account web pages: How to avoid the old cache affecting the user experience after version update?
Mar 04, 2025 pm 12:32 PM
The official account web page update cache, this thing is simple and simple, and it is complicated enough to drink a pot of it. You worked hard to update the official account article, but the user still opened the old version. Who can bear the taste? In this article, let’s take a look at the twists and turns behind this and how to solve this problem gracefully. After reading it, you can easily deal with various caching problems, allowing your users to always experience the freshest content. Let’s talk about the basics first. To put it bluntly, in order to improve access speed, the browser or server stores some static resources (such as pictures, CSS, JS) or page content. Next time you access it, you can directly retrieve it from the cache without having to download it again, and it is naturally fast. But this thing is also a double-edged sword. The new version is online,
How do I use HTML5 form validation attributes to validate user input?
Mar 17, 2025 pm 12:27 PM
The article discusses using HTML5 form validation attributes like required, pattern, min, max, and length limits to validate user input directly in the browser.
What are the best practices for cross-browser compatibility in HTML5?
Mar 17, 2025 pm 12:20 PM
Article discusses best practices for ensuring HTML5 cross-browser compatibility, focusing on feature detection, progressive enhancement, and testing methods.
How to efficiently add stroke effects to PNG images on web pages?
Mar 04, 2025 pm 02:39 PM
This article demonstrates efficient PNG border addition to webpages using CSS. It argues that CSS offers superior performance compared to JavaScript or libraries, detailing how to adjust border width, style, and color for subtle or prominent effect
What is the purpose of the <datalist> element?
Mar 21, 2025 pm 12:33 PM
The article discusses the HTML <datalist> element, which enhances forms by providing autocomplete suggestions, improving user experience and reducing errors.Character count: 159
What is the purpose of the <meter> element?
Mar 21, 2025 pm 12:35 PM
The article discusses the HTML <meter> element, used for displaying scalar or fractional values within a range, and its common applications in web development. It differentiates <meter> from <progress> and ex
How do I use the HTML5 <time> element to represent dates and times semantically?
Mar 12, 2025 pm 04:05 PM
This article explains the HTML5 <time> element for semantic date/time representation. It emphasizes the importance of the datetime attribute for machine readability (ISO 8601 format) alongside human-readable text, boosting accessibilit
What is the purpose of the <progress> element?
Mar 21, 2025 pm 12:34 PM
The article discusses the HTML <progress> element, its purpose, styling, and differences from the <meter> element. The main focus is on using <progress> for task completion and <meter> for stati
