When is css applied

If the user selects the "big print" style, only the alternate style sheet "bigprint. A cascade may include style sheets applicable to different media. The user agent is then responsible for filtering out those style sheets that do not apply to the current medium.

In the following example, we define a cascade where the "corporate" style sheet is provided in several versions: one suited to printing, one for screen use and one for speech-based browsers useful, say, when reading email in the car.

The "techreport" stylesheet applies to all media. The color rule defined by the STYLE element is used for print and screen but not for aural rendering. When the user agent wants to render a document, it needs to find values for style properties, e. The exact mechanism depends on the style sheet language, but the following description is generally applicable:. The cascading mechanism is used when a number of style rules all apply directly to an element. The mechanism allows the user agent to sort the rules by specificity, to determine which rule to apply.

If no rule can be found, the next step depends on whether the style property can be inherited or not. Not all properties can be inherited.

For these properties the style sheet language provides default values for use when there are no explicit rules for a particular element. If the property can be inherited, the user agent examines the immediately enclosing element to see if a rule applies to that. This process continues until an applicable rule is found. This mechanism allows style sheets to be specified compactly.

Some style sheet languages support syntax intended to allow authors to hide the content of STYLE elements from non-conforming user agents. This example illustrates for CSS how to comment out the content of STYLE elements to ensure that older, non-conforming user agents will not render them as text. This section only applies to user agents conforming to versions of HTTP that define a Link header field. Note that HTTP 1.

Web server managers may find it convenient to configure a server so that a style sheet will be applied to a group of pages. For instance,. It is possible to specify several alternate styles using multiple Link headers, and then use the rel attribute to determine the default style. In the following example, "compact" is applied by default since it omits the "alternate" keyword for the rel attribute.

This should also work when HTML documents are sent by email. Some email agents can alter the ordering of [RFC] headers. To protect against this affecting the cascading order for style sheets specified by Link headers, authors can use header concatenation to merge several instances of the same header field. The quote marks are only needed when the attribute values include whitespace. Use SGML entities to reference characters that are otherwise not permitted within HTTP or email headers, or that are likely to be affected by transit through gateways.

This CSS example sets color and font size information for the text in a specific paragraph. The first and most important thing to understand is that browsers cannot begin painting a page until all CSS is downloaded. Keep in mind, the W3C spec says that CSS links are only allowed in the head, so when you start linking to stylesheets in the body tag as you did, different browsers will handle this situation differently.

To quote the Google article linked below:. As the browser parses HTML, it constructs an internal document tree representing all the elements to be displayed.

It then matches elements to styles specified in various stylesheets, according to the standard CSS cascade, inheritance, and ordering rules. This is because the CSS is all downloaded first, then when it encountered your element it only applied the red style, because of how the cascade works.

While I cannot say exactly why this happened, I imagine the browser did not look for CSS in the body tag, began painting, encountered the body CSS, then repainted.

I would honestly be more worried about JS caused repaints. But if you have a very large DOM, it makes sense to structure your CSS in such a way that you are not causing reflows due to odd positioning. Matt gave you some good links covering that issue Some good resources:. I am not sure about the marked answer. I doubt it's correctness. Note that it doesn't apply any styles to the document when the browser is downloading the CSS file.

After this it creates another tree called Render tree which builds all the objects which should be displayed, as rectangle boxes.

Only after completing the render tree it starts painting on to the screen. You can use the chrome's Developer console to check these. Use the timeline tab to see all this.

A sample of the timeline image is shown here. The link i posted at the beginning of this answer explains everything. How are we doing? Please help us improve Stack Overflow. Take our short survey. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. How is CSS applied by the browser, and are repaints affected by it? Ask Question. Asked 10 years, 3 months ago. Active 1 year, 2 months ago. Viewed 11k times.

Summary: Is all CSS content downloaded before any of it is applied? Improve this question. HoldOffHunger 13k 8 8 gold badges 63 63 silver badges bronze badges. Wesley Murch Wesley Murch Everything is "namespaced", or using specific enough selectors where the order can be swapped in many cases.

I've always included the "less relevant" CSS last, thinking that the styles would be applied last, and that having them be first would make the more important stuff page layout or common classes for instance be evaluated later. The text color in the div will be blue. For those of you that are not so mathematically inclined, there's always this graphical method.

We've already talked about how there can be many different sources of CSS styles. How do we know which one will be used? In CSS, styles sheets cascade by order of importance. If rules in different style sheets conflict with one another, the rule from the most important style sheet wins. Below is a list of possible sources of a CSS rule. They are listed by order of importance. As the creator of the style sheet, you're the author.

We've already seen the cascade in action. All browsers have a default style sheet, which is designated as the least important. Warning: In CSS and other web standards , it has been agreed that US spelling is the standard where there is language variation or uncertainty. For example, colour should be spelled color , as colour will not work. While most values are relatively simple keywords or numeric values, there are some values that take the form of a function.

A function consists of the function name, and parentheses to enclose the values for the function. The result of the calculation isn't something that can be computed in advance and entered as a static value. Another example would be the various values for transform , such as rotate. CSS rules pronounced "at-rules" provide instruction for what CSS should perform or how it should behave. Some rules are simple with just a keyword and a value. For example, import imports a stylesheet into another CSS stylesheet:.

One common rule that you are likely to encounter is media , which is used to create media queries. Media queries use conditional logic for applying CSS styling. However, a media query follows that defines a blue background if the browser viewport is wider than 30em.

See if you can add a media query that changes styles based on the viewport width. Change the width of your browser window to see the result. Some properties like font , background , padding , border , and margin are called shorthand properties. This is because shorthand properties set several values in a single line. Later in the course, you will encounter many other examples of shorthand properties.

Try using the declarations above in your own CSS exercise to become more familiar with how it works. You can also experiment with different values. Warning: One less obvious aspect of using CSS shorthand is how omitted values reset.

A value not specified in CSS shorthand reverts to its initial value. This means an omission in CSS shorthand can override previously set values. As with any coding work, it is best practice to write comments along with CSS. This helps you to remember how the code works as you come back later for fixes or enhancement. It also helps others understand the code. In the example below, comments mark the start of distinct sections of code. This helps to navigate the codebase as it gets larger.

With this kind of commenting in place, searching for comments in your code editor becomes a way to efficiently find a section of code. In the example below, the rules for. White space means actual spaces, tabs and new lines.

The value of white space is how it can improve readability. This is arguably a good way to write CSS.