Understanding the Nuances of Nested Vertical Margin Collapses
In CSS, the concept of margin collapsing plays a crucial role in determining the spacing between elements on a web page. When margins of vertically adjacent elements touch, they collapse into a single margin, resulting in unexpected behavior. Nested vertical margin collapses further complicate this behavior.
Mechanism of Nested Margin Collapses
When two elements are nested within each other and their margins touch, the following two rules apply:
- Margin Collapse: The margins collapse into a single margin with the maximum height of the individual margins.
- Snuggling: The inner element "snuggles" against the top border of its container, eliminating any space between the elements.
For instance, consider the following HTML and CSS:
<code class="html"><div id="outer"> <div id="inner"> A </div> </div></code>
<code class="css">#outer { margin-top: 10px; background: blue; height: 100px; } #inner { margin-top: 20px; background: red; height: 33%; width: 33%; }</code>
In this case, the margins collapse to 20px (the maximum of 10px and 20px), and the inner div snuggles up to the top of the outer div.
However, if any content or border separates the two margins, the collapse is lost. This can occur when adding non-breaking whitespace or a border between the elements, as demonstrated below:
<code class="html"><div id="outer"> <div id="inner"> A </div> </div></code>
Note: This behavior does not apply to elements positioned as absolute, fixed, or floated.
The above is the detailed content of How Do Nested Vertical Margin Collapses Work in CSS?. For more information, please follow other related articles on the PHP Chinese website!

Hot AI Tools

Undress AI Tool
Undress images for free

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

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

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

There are three ways to selectively include CSS on a specific page: 1. Inline CSS, suitable for pages that are not frequently accessed or require unique styles; 2. Load external CSS files using JavaScript conditions, suitable for situations where flexibility is required; 3. Containment on the server side, suitable for scenarios using server-side languages. This approach can optimize website performance and maintainability, but requires balance of modularity and performance.

CSS blocks page rendering because browsers view inline and external CSS as key resources by default, especially with imported stylesheets, header large amounts of inline CSS, and unoptimized media query styles. 1. Extract critical CSS and embed it into HTML; 2. Delay loading non-critical CSS through JavaScript; 3. Use media attributes to optimize loading such as print styles; 4. Compress and merge CSS to reduce requests. It is recommended to use tools to extract key CSS, combine rel="preload" asynchronous loading, and use media delayed loading reasonably to avoid excessive splitting and complex script control.

In the following tutorial, I will show you how to create Lottie animations in Figma. We'll use two colorful designs to exmplify how you can animate in Figma, and then I'll show you how to go from Figma to Lottie animations. All you need is a free Fig

We put it to the test and it turns out Sass can replace JavaScript, at least when it comes to low-level logic and puzzle behavior. With nothing but maps, mixins, functions, and a whole lot of math, we managed to bring our Tangram puzzle to life, no J

ThebestapproachforCSSdependsontheproject'sspecificneeds.Forlargerprojects,externalCSSisbetterduetomaintainabilityandreusability;forsmallerprojectsorsingle-pageapplications,internalCSSmightbemoresuitable.It'scrucialtobalanceprojectsize,performanceneed

No,CSSdoesnothavetobeinlowercase.However,usinglowercaseisrecommendedfor:1)Consistencyandreadability,2)Avoidingerrorsinrelatedtechnologies,3)Potentialperformancebenefits,and4)Improvedcollaborationwithinteams.

CSSCounters is a tool for creating automatic numbers. 1. Basic usage: define and operate counters through counter-reset and counter-increment, such as "SectionX." before h2. 2. Advanced usage: Use nested counters to create complex numbers, such as chapter and section numbers. 3. Notes: Ensure the counter is reset correctly, optimize performance, and simplify counter logic. 4. Best practice: clear naming, define counters in CSS, and use counter-increment and counter-reset reasonably.

CSSismostlycase-insensitive,butURLsandfontfamilynamesarecase-sensitive.1)Propertiesandvalueslikecolor:red;arenotcase-sensitive.2)URLsmustmatchtheserver'scase,e.g.,/images/Logo.png.3)Fontfamilynameslike'OpenSans'mustbeexact.
