


Content Overlapping by Overlapping Elements: Understanding the Puzzle
Introduction
In this context, we have two divs without any complex styling (simply background-color). We are manipulating the second div to overlap the first one by applying a negative margin-top. However, instead of seeing one element completely overlapping the other, we find the second div sliding between the content and the background of the first div, exhibiting an unexpected behavior.
The Painting Order
To understand this behavior, we need to delve into the intricacies of the painting order in browsers. The painting order for elements within a stacking context follows a predefined sequence:
- Background color of the element, even if it's the root element.
- Background image of the element, even if it's the root element.
- Content of the element, such as text and images, painted from bottom to top.
- Background and border of child elements.
Explaining the Overlap
In our example, when the second div overlaps the first, the following painting sequence occurs:
- Background color of the second div is painted over the first div's background.
- Content of the first div is painted.
- Content of the second div is painted on top of the first div's content.
Since the content of the first div is painted before the background of the second div, the text appears to be positioned above the green background, creating the illusion that the second div is sliding between them.
Changing the Behavior
While the default painting order can lead to such situations, it's possible to modify the behavior by setting the opacity of the overlapping element to a value less than 1. This triggers the opacity painting step before the content painting step, ensuring the overlapping element's background appears beneath its content.
In our example, adding opacity: 0.9999 to the second div leads to the expected behavior, where the green background completely covers the first div's content.
Reference
For a detailed explanation of the CSS paint order, refer to the official W3C documentation:
https://www.w3.org/TR/css-backgrounds-3/#box-painting
The above is the detailed content of Why Does a Negatively Margined Div Appear to Slide *Between* the Content and Background of Another Div?. For more information, please follow other related articles on the PHP Chinese website!

CSS Grid is a powerful tool for creating complex, responsive web layouts. It simplifies design, improves accessibility, and offers more control than older methods.

Article discusses CSS Flexbox, a layout method for efficient alignment and distribution of space in responsive designs. It explains Flexbox usage, compares it with CSS Grid, and details browser support.

The article discusses techniques for creating responsive websites using CSS, including viewport meta tags, flexible grids, fluid media, media queries, and relative units. It also covers using CSS Grid and Flexbox together and recommends CSS framework

The article discusses the CSS box-sizing property, which controls how element dimensions are calculated. It explains values like content-box, border-box, and padding-box, and their impact on layout design and form alignment.

Article discusses creating animations using CSS, key properties, and combining with JavaScript. Main issue is browser compatibility.

Article discusses using CSS for 3D transformations, key properties, browser compatibility, and performance considerations for web projects.(Character count: 159)

The article discusses using CSS gradients (linear, radial, repeating) to enhance website visuals, adding depth, focus, and modern aesthetics.

Article discusses pseudo-elements in CSS, their use in enhancing HTML styling, and differences from pseudo-classes. Provides practical examples.


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

SublimeText3 Chinese version
Chinese version, very easy to use

EditPlus Chinese cracked version
Small size, syntax highlighting, does not support code prompt function

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.

WebStorm Mac version
Useful JavaScript development tools

PhpStorm Mac version
The latest (2018.2.1) professional PHP integrated development tool
