What is css cascading

css cascading is a basic feature of CSS. It is an algorithm that defines how to merge attribute values ​​​​from multiple sources; CSS cascading means that when the CSS style configures the same attribute for the same element, it is based on cascading. Rules are used to handle conflicts, choosing to apply the attribute specified by the CSS selector with the highest weight.

The operating environment of this article: Windows7 system, HTML5&&CSS3 version, Dell G3 computer.

What is css cascading?

Cascading is a fundamental feature of CSS, an algorithm that defines how to combine property values ​​from multiple sources. It is at the core of CSS, and the full name of CSS, Cascading Style Sheets, emphasizes this point.

CSS cascading means that when the CSS style configures the same attribute for the same element, it handles conflicts according to the cascading rules (weight) and selects the attribute specified by the CSS selector with high weight. It is also generally described as The ones with higher weights cover the ones with lower weights, so it is also called stacking.

Each CSS selector will have a weight. When two selectors configure the same attribute of the same element at the same time (for example, one sets color: red and the other color: black), a conflict will occur, and The solution to resolve the conflict is the weight of the CSS selector. The one with higher weight overrides the one with lower weight.

Cascading means that the style of the upper-level tag will be automatically inherited to all its lower-level tags. For example, the font style set for the tag selector set for will be automatically applied to the tags under

, unless

overrides the related style by overriding it.

Stacking refers to the priority of styles. When a conflict occurs, the one with higher priority shall prevail:

• Developer Style>Reader Style>Browse Selector style (unless using the !important tag)

• ##id selector > (pseudo) class selector > element selector

• Weight At the same time, take the style defined later

The CSS cascading algorithm expects to set the correct value for the CSS property by selecting CSS declarations. CSS declarations can come from different sources:

1. The browser will have a basic style sheet to set the default style for any web page. These styles are collectively called **User Agent Styles**. Some browsers do this by using real style sheets, while others emulate it through code, but in either case it should be undetectable.

And some browsers allow users to modify the user agent style. Although the HTML standard places many restrictions on user agent styles, browsers still have a lot to do, and there will be significant differences between different browsers.

In order to reduce development costs and reduce the basic environment required to run the style sheet, web developers usually use a CSS reset style sheet to force common attribute values ​​to a certain state.

2. The author of the web page can define the style of the document. This is the most common style sheet. In most cases, multiple style sheets of this type will be defined, which constitute the visual and experience of the website, that is, the theme.

3. Readers, as browser users, can use custom style sheets to customize their experience.

Although CSS styles come from these different sources, their scopes overlap, and the cascading algorithm defines how they interact.

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