Journal tags: inline

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sparkline

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.

Inlining SVG background images in CSS with custom properties

Here’s a tiny lesson that I picked up from Trys that I’d like to share with you…

I was working on some upcoming changes to the Clearleft site recently. One particular component needed some SVG background images. I decided I’d inline the SVGs in the CSS to avoid extra network requests. It’s pretty straightforward:

.myComponent {
    background-image: url('data:image/svg+xml;utf8,<svg> ... </svg>');
}

You can basically paste your SVG in there, although you need to a little bit of URL encoding: I found that converting # to %23 to was enough for my needs.

But here’s the thing. My component had some variations. One of the variations had multiple background images. There was a second background image in addition to the first. There’s no way in CSS to add an additional background image without writing a whole background-image declaration:

.myComponent--variant {
    background-image: url('data:image/svg+xml;utf8,<svg> ... </svg>'), url('data:image/svg+xml;utf8,<svg> ... </svg>');
}

So now I’ve got the same SVG source inlined in two places. That negates any performance benefits I was getting from inlining in the first place.

That’s where Trys comes in. He shared a nifty technique he uses in this exact situation: put the SVG source into a custom property!

:root {
    --firstSVG: url('data:image/svg+xml;utf8,<svg> ... </svg>');
    --secondSVG: url('data:image/svg+xml;utf8,<svg> ... </svg>');
}

Then you can reference those in your background-image declarations:

.myComponent {
    background-image: var(--firstSVG);
}
.myComponent--variant {
    background-image: var(--firstSVG), var(--secondSVG);
}

Brilliant! Not only does this remove any duplication of the SVG source, it also makes your CSS nice and readable: no more big blobs of SVG source code in the middle of your style sheet.

You might be wondering what will happen in older browsers that don’t support CSS custom properties (that would be Internet Explorer 11). Those browsers won’t get any background image. Which is fine. It’s a background image. Therefore it’s decoration. If it were an important image, it wouldn’t be in the background.

Progressive enhancement, innit?

Whatever works for you

I was one of the panelists on the most recent episode of the Shop Talk Show along with Nicole, Colin Megill, and Jed Schmidt. The topic was inline styles. Well, not quite. That’s not a great term to describe the concept. The idea is that you apply styling directly to DOM nodes using JavaScript, instead of using CSS selectors to match up styles to DOM nodes.

It’s an interesting idea that I could certainly imagine being useful in certain situations such as dynamically updating an interface in real time (it feels a bit more “close to the metal” to reflect the state updates directly rather than doing it via class swapping). But there are many, many other situations where the cascade is very useful indeed.

I expressed concern that styling via JavaScript raises the barrier to styling from a declarative language like CSS to a programming language (although, as they pointed out, it’s more like moving from CSS to JSON). I asked whether it might not be possible to add just one more layer of abstraction so that people could continue to write in CSS—which they’re familiar with—and then do JavaScript magic to match those selectors, extract those styles, and apply them directly to the DOM nodes. Since recording the podcast, I came across Glen Maddern’s proposal to do exactly that. It makes sense to me try to solve the perceived problems with CSS—issues of scope and specificity—without asking everyone to change the way they write.

In short, my response was “hey, like, whatever, it’s cool, each to their own.” There are many, many different kinds of websites and many, many different ways to make them. I like that.

So I was kind of surprised by the bullishness of those who seem to honestly believe that this is the way to build on the web, and that CSS will become a relic. At one point I even asked directly, “Do you really believe that CSS is over? That all styles will be managed through JavaScript from here on?” and received an emphatic “Yes!” in response.

I find that a little disheartening. Chris has written about the confidence of youth:

Discussions are always worth having. Weighing options is always interesting. Demonstrating what has worked (and what hasn’t) for you is always useful. There are ways to communicate that don’t resort to dogmatism.

There are big differences between saying:

  • You can do this,
  • You should do this, and
  • You must do this.

My take on the inline styles discussion was that it fits firmly in the “you can do this” slot. It could be a very handy tool to have in your toolbox for certain situations. But ideally your toolbox should have many other tools. When all you have is a hammer, yadda, yadda, yadda, nail.

I don’t think you do your cause any favours by jumping straight to the “you must do this” stage. I think that people are more amenable to hearing “hey, here’s something that worked for me; maybe it will work for you” rather than “everything you know is wrong and this is the future.” I certainly don’t think that it’s helpful to compare CSS to Neanderthals co-existing with JavaScript Homo Sapiens.

Like I said on the podcast, it’s a big web out there. The idea that there is “one true way” that would work on all possible projects seems unlikely—and undesirable.

“A ha!”, you may be thinking, “But you yourself talk about progressive enhancement as if it’s the one try way to build on the web—hoisted by your own petard.” Actually, I don’t. There are certainly situations where progressive enhancement isn’t workable—although I believe those cases are rarer than you might think. But my over-riding attitude towards any questions of web design and development is:

It depends.