Tags: specificity

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Monday, September 20th, 2021

The Future of CSS: Cascade Layers (CSS @layer) – Bram.us

This is a really in-depth explanation from Bramus of the upcoming @layer rules in CSS, from the brilliant minds of Miriam, fantasai and Tab.

Basically, you’ll be able to scope styles, and you get to define the context for that scoping. So all those CSS-in-JS folks who don’t appreciate the cascade will have a mechanism to get encapsulated styles.

I can see this being very handy for big complex codebases with lots of people on the team.

Saturday, May 22nd, 2021

Should DevTools teach the CSS cascade?

In a break with Betteridge’s law, I think the answer here is “yes.”

Tuesday, December 15th, 2020

Cascading Style Sheets

There are three ways—that I know of—to associate styles with markup.

External CSS

This is probably the most common. Using a link element with a rel value of “stylesheet”, you point to a URL using the href attribute. That URL is a style sheet that is applied to the current document (“the relationship of the linked resource it is that is a ‘stylesheet’ for the current document”).

<link rel="stylesheet" href="/path/to/styles.css">

In theory you could associate a style sheet with a document using an HTTP header, but I don’t think many browsers support this in practice.

You can also pull in external style sheets using the @import declaration in CSS itself, as long as the @import rule is declared at the start, before any other styles.

@import url('/path/to/more-styles.css');

When you use link rel="stylesheet" to apply styles, it’s a blocking request: the browser will fetch the style sheet before rendering the HTML. It needs to know how the HTML elements will be painted to the screen so there’s no point rendering the HTML until the CSS is parsed.

Embedded CSS

You can also place CSS rules inside a style element directly in the document. This is usually in the head of the document.

<style>
element {
    property: value;
}
</style>

When you embed CSS in the head of a document like this, there is no network request like there would be with external style sheets so there’s no render-blocking behaviour.

You can put any CSS inside the style element, which means that you could use embedded CSS to load external CSS using an @import statement (as long as that @import statement appears right at the start).

<style>
@import url('/path/to/more-styles.css');
element {
    property: value;
}
</style>

But then you’re back to having a network request.

Inline CSS

Using the style attribute you can apply CSS rules directly to an element. This is a universal attribute. It can be used on any HTML element. That doesn’t necessarily mean that the styles will work, but your markup is never invalidated by the presence of the style attribute.

<element style="property: value">
</element>

Whereas external CSS and embedded CSS don’t have any effect on specificity, inline styles are positively radioactive with specificity. Any styles applied this way are almost certain to over-ride any external or embedded styles.

You can also apply styles using JavaScript and the Document Object Model.

element.style.property = 'value';

Using the DOM style object this way is equivalent to inline styles. The radioactive specificity applies here too.

Style declarations specified in external style sheets or embedded CSS follow the rules of the cascade. Values can be over-ridden depending on the order they appear in. Combined with the separate-but-related rules for specificity, this can be very powerful. But if you don’t understand how the cascade and specificity work then the results can be unexpected, leading to frustration. In that situation, inline styles look very appealing—there’s no cascade and everything has equal specificity. But using inline styles means foregoing a lot of power—you’d be ditching the C in CSS.

A common technique for web performance is to favour embedded CSS over external CSS in order to avoid the extra network request (at least for the first visit—there are clever techniques for caching an external style sheet once the HTML has already loaded). This is commonly referred to as inlining your CSS. But really it should be called embedding your CSS.

This language mix-up is not a hill I’m going to die on (that hill would be referring to blog posts as blogs) but I thought it was worth pointing out.

Friday, July 10th, 2020

What is CSS Specificity? Sarah Chima - Front-End Developer

An excellent and clear explanation of specificity in CSS.

Wednesday, January 22nd, 2020

The CSS Cascade

This is a wonderful interactive explanation of the way CSS hierarchy works—beautiful!

Tuesday, June 12th, 2018

Resilient, Declarative, Contextual

This is really good breakdown of what’s different about CSS (compared to other languages).

These differences may feel foreign, but it’s these differences that make CSS so powerful. And it’s my suspicion that developers who embrace these things, and have fully internalized them, tend to be far more proficient in CSS.

Saturday, September 23rd, 2017

[selectors] Functional pseudo-class like :matches() with 0 specificity · Issue #1170 · w3c/csswg-drafts

A really interesting proposal from Lea that would allow CSS authors to make full use of selectors but without increasing specificity. Great thoughts in the comments too.

Saturday, April 15th, 2017

The invisible parts of CSS · MadebyMike

This is a really clear explanation of how CSS works.

Tuesday, October 21st, 2014

Axiomatic CSS and Lobotomized Owls · An A List Apart Article

I’m quite intrigued by the thinking behind this CSS selector of Heydon’s.

* + * {
    margin-top: 1.5em;
}

I should try it out and see how it feels.