The heading and paragraph do not, however, inherit the background but instead default to transparent , so the net visual result is white text displayed on a blue background. Save and reload the document: this rule sets the font size of the heading. You can force inheritance — even for properties that are not inherited by default — by using the inherit keyword. Use this strategy with care, however, since Microsoft Internet Explorer versions up to and including version 7 do not support this keyword.
The following rule will make all paragraphs inherit all background properties from their parents:. Forcing inheritance is not a common practice. As an example, consider a typical navigation menu:. Here the background color of the whole list is set to blue in the rule for nav. This also sets the foreground color to white, and this property is inherited by each list item and each link.
Of course, you can specify the border color as white and the link text color as white, but the beauty of letting inheritance do the job is that it is only necessary to update one place to change the colors if you decide to update the color scheme later. CSS an acronym of Cascading Style Sheets, so it is not a surprise that the cascade is an important concept. It is the mechanism that controls the end result when multiple, conflicting CSS declarations apply to the same element.
There are three main concepts that control the order in which CSS declarations are applied:. Importance is the most … er … important.
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If two declarations have the same importance, the specificity of the rules decide which one will apply. If the rules have the same specificity, then source order controls the outcome. The importance of a CSS declaration depends on where it is specified. The conflicting declarations will be applied in the following order, with later declarations overriding earlier ones:.
A user agent style sheet is the built-in style sheet of the browser. Every browser has its default rules for how to display various HTML elements if no style is specified by the user or designer of the page. For instance, unvisited links are usually blue and underlined. A user style sheet is a style sheet that the user has specified. Not all browsers support user style sheets, but they can be very useful, especially for users with certain types of disabilities. For instance, a dyslexic person can have a user style sheet that specifies certain fonts and colors to help them read more easily.
The opposite is important declarations, which are declarations followed by an!
A dyslexic user might, for instance, want all text to be displayed in Comic Sans MS if he finds that font easier to read. He could then have a user style sheet containing the following rule:. Important declarations in a user style sheet will trump everything else, which is logical. There is no way we could know if a user has a user style sheet defined that will override our CSS.
If they do, they probably have a very good reason for doing so, anyway.
Cascade, Specificity and Inheritance Definitions and Notes
Specificity is something every CSS author needs to understand and to think about. The specificity of a selector can easily be calculated, as we shall see below. After a bit of counting, we can thus string those four components together to get the specificity for any rule. There is one attribute selector. Note 2: There is a huge difference in specificity between an id selector and an attribute selector that happens to refer to an id attribute.
Although they match the same element, they have very different specificities. Now save both files and reload the document in your browser; there should now be two paragraphs with cyan text. However, inheritance has the lowest priority among styling methods. In other words, if a child has a rule that is specific to it, then the inherited value will be ignored, even though the inherited value may have an important keyword.
The following is an example:. See the Pen Child ignores inline inheritance with! For SVG elements, we can also apply styles using inline attributes, where those have the second lowest priority in the cascade. This means the CSS rules in a stylesheet will be able to override them. Most SVG editors use inline attributes for portability; that is, the ability to copy some elements and paste them elsewhere without losing the attributes.
Users can then use the resultant SVG and style its elements using an external stylesheet.
Stylesheets are divided into two flavors: external and embedded :. Embedded styles have the same priority as external stylesheets. Therefore, if you have the same CSS rules, ordering rules applies. All stylesheets follow ordering rules , where files that are defined later, will have higher priority than those defined earlier.
The "C" in CSS: The Cascade | CSS-Tricks
In this example, stylesheet How you select your elements will also determine which rules are applied, whereby tags e. In the example above, if you have a div element with both. Specificity still has higher priority and will be applied. Inline styles have the second highest priority , just below the! This means that inline styles are only overridden by the important keyword and nothing else.
Within inline styles, normal ordering rules applies, from left-to-right and top-to-bottom.
- The cascade.
- The Devil That You Dare.
- Handbook of Free Gymnastics.
- Cascade, Specificity and Inheritance Definitions and Notes;
Speaking of the! In other words, it wields incredible powers. In the example above, without the important keyword, the div would have a red border because inline styling has higher priority than embedded styles. But, with the important keyword, the div border becomes orange, because the important keyword has higher priority than inline styling. Chris has some thoughts on situations where it makes sense to use it. Without the important keyword, this div border will be blue, because classes have higher priority than tags in specificity. Adding the important keyword to the tag rules tells the element to ignore the cascade and take precedence over the class rules.
See the Pen! Return to Book Page. Exactly how does the "cascade" in Cascading Style Sheets work? This concise guide demonstrates the power and simplicity of CSS selectors for applying style rules to different web page elements. You'll learn how your page's presentation depends on a multitude of style rules and the complex ways they function--and sometimes collide--within the document's structure.
This guide Exactly how does the "cascade" in Cascading Style Sheets work? When you purchase either the print or the ebook edition of Selectors, Specificity, and the Cascade , you'll receive a significant discount on the entire Definitive Guide when it's released. Why wait when you can learn how to use selectors and other key CSS 3 features right away?
Learn how to create CSS rules that apply to a large number of similar elements Group rules to make style sheets smaller and download times faster Understand how elements inherit styles from their parents Discover how reader and browser preferences affect your page presentation Examine specificity--the method browsers use to choose between two conflicting style rules Get a handle on how specificity and inheritance combine to form the cascade Get details on all of the CSS3 selectors Get A Copy. More Details Other Editions 5. Friend Reviews.
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