Absolute positioning of CSS_html/css_WEB-ITnose-HTML Tutorial-php.cn

Home

Web Front-end

HTML Tutorial

Absolute positioning of CSS_html/css_WEB-ITnose

WBOYWBOYWBOYWBOYWBOYWBOYWBOYWBOYWBOYWBOYWBOYWBOYWB

Jun 24, 2016 pm 12:31 PM

Absolute positioning of CSS:
1. Basic concept:
If relative positioning does not break away from the document flow and offset relative to the object itself is a bit confusing, then absolute positioning is definitely It cuts the knot quickly, because absolute positioning can make an object break away from the normal document flow, as if it is floating above the normal document flow, and position it relative to the element containing the object. Of course, this positioning relative to the element also varies in different situations. different.
2. How to set an element to absolute positioning:
Add the following attributes to the object to set the object to absolute positioning:

position:absolute; 或者 position:fixed

3. Positioning reference object:
You can use the top attribute and left attribute to set the offset of the absolutely positioned object.
Although absolute positioning is separated from the document flow, it also requires a reference object for positioning, but the reference object is different in different situations.
1. If the top or left attribute value is not set, then the positioning reference object of the corresponding orientation is the first-level parent element of this object. The code example is as follows:

<!DOCTYPE html> <html> <head> <meta charset=" utf-8"> <meta name="author" content="http://www.softwhy.com/" /> <title>CSS的绝对定位-蚂蚁部落</title>  <style type="text/css"> body { margin:20px; } #grandfather { width:330px; height:300px; background-color:#F90; } #father { width:200px; height:200px; background-color:green; margin-left:50px; } #children { width:100px; height:100px; background-color:red; float:right; } #inner { width:50px; height:50px; background-color:blue; position:absolute; top:10px; } </style> </head> <body> <div id="grandfather"> <div id="father">   <div id="children">    <div id="inner"></div>   </div> </div> </div> </body> </html>

In the above code, since the inner element uses absolute positioning and the left attribute value is not set, the positioning reference object in the horizontal direction is the first-level parent element children of the inner element. Of course, if the top attribute value is not set, the vertical positioning reference object is also children.
2. If the left or top attribute value is set:
1). If the ancestor element uses positioning, then the positioning reference object of the corresponding direction of this object is this ancestor element. If the ancestor element does not use positioning, Positioned, then the positioning reference object in the corresponding direction is the browser client area. The code example is as follows:
Example 1:

<!DOCTYPE html> <html> <head> <meta charset=" utf-8"> <meta name="author" content="http://www.softwhy.com/" /> <title>CSS的绝对定位-蚂蚁部落</title>  <style type="text/css"> body { margin:20px; } #grandfather { width:330px; height:300px; background-color:#F90; } #father { width:200px; height:200px; background-color:green; margin-left:50px; position:relative; } #children { width:100px; height:100px; background-color:red; float:right; } #inner { width:50px; height:50px; background-color:blue; position:absolute; left:10px; top:10px; } </style> </head> <body> <div id="grandfather"> <div id="father">   <div id="children">    <div id="inner"></div>   </div> </div> </div> </body> </html>

The above code, the inner element uses absolute Positioning, and its ancestor element father adopts relative positioning, then its positioning reference object is father.
Example 2:

<!DOCTYPE html> <html> <head> <meta charset=" utf-8"> <meta name="author" content="http://www.softwhy.com/" /> <title>CSS的绝对定位-蚂蚁部落</title>  <style type="text/css"> body { margin:20px; } #grandfather { width:330px; height:300px; background-color:#F90; } #father { width:200px; height:200px; background-color:green; margin-left:50px; } #children { width:100px; height:100px; background-color:red; float:right; } #inner { width:50px; height:50px; background-color:blue; position:absolute; top:10px; } </style> </head> <body> <div id="grandfather"> <div id="father">   <div id="children">    <div id="inner"></div>   </div> </div> </div> </body> </html>

In the above code, the inner element uses absolute positioning, and its ancestor elements do not use Positioned, then the vertical positioning reference object is the window. Since the left attribute value is not set, the horizontal positioning reference object is its first-level parent element children.
4. Absolutely positioned elements break away from the document flow:
As mentioned at the beginning, absolute positioning can make an element break away from the document flow, then elements in the surrounding document flow can occupy the space when this element does not break away from the document flow. Location.
The code example is as follows:

<!DOCTYPE html> <html> <head> <meta charset=" utf-8"> <meta name="author" content="http://www.softwhy.com/" /> <title>CSS的绝对定位-蚂蚁部落</title>  <style type="text/css"> div { text-align:center; line-height:100px; } .father { width:400px; height:400px; background-color:green; margin:50px; } .first { width:100px; height:100px; background-color:red; position:absolute; } .second { width:120px; height:120px; background-color:blue; } </style> </head> <body> <div class="father"> <div class="first">first</div> <div class="second">second</div> </div> </body> </html>

In the above code, since the first element is out of the document flow, the second element can Occupy the position that the original first element should have occupied.
Special note: Positioned elements are often used together with the z-index attribute. For details, please refer to the detailed usage of the z-index attribute in CSS

Statement

The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn

What is the purpose of HTML tags?Apr 28, 2025 am 12:02 AM

HTMLtagsareessentialforstructuringwebpages,enhancingaccessibility,SEO,andperformance.1)Theyareenclosedinanglebracketsandusedinpairstocreateahierarchicalstructure.2)SemantictagslikeandimproveuserexperienceandSEO.3)Creativetagslikeenabledynamicgraphics

What are self-closing tags? Give an example.Apr 27, 2025 am 12:04 AM

Self-closingtagsinHTMLandXMLaretagsthatclosethemselveswithoutneedingaseparateclosingtag,simplifyingmarkupstructureandenhancingcodingefficiency.1)TheyareessentialinXMLforelementswithoutcontent,ensuringwell-formeddocuments.2)InHTML5,usageisflexiblebutr

Beyond HTML: Essential Technologies for Web DevelopmentApr 26, 2025 am 12:04 AM

To 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 AM

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.

How can you validate your HTML code?Apr 24, 2025 am 12:04 AM

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 vs. CSS and JavaScript: Comparing Web TechnologiesApr 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 as a Markup Language: Its Function and PurposeApr 22, 2025 am 12:02 AM

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 of HTML, CSS, and JavaScript: Web Development TrendsApr 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.

See all articles