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?

Get the screen width & height without JavaScript

Clever!

Retrofitting fluid typography | Clagnut by Richard Rutter

Here’s a taste of what Rich will be delivering at Patterns Day on Thursday—can’t wait!

Offloading JavaScript With Custom Properties: HeydonWorks

With classes, we can send CSS static values but with custom properties we can send dynamic ones, which is a major shift in the way we can style state. This is something that has been true for some time—and is extremely well supported—but sometimes it takes solving a small real-world problem to make you appreciate the value of it.

I think we still haven’t come to fully appreciate the superpower of custom properties: dynamic values that are shared between CSS and JavaScript.

On Container Queries, Responsive Images, and JPEG-XL – Cloud Four

Container queries can’t be used in the sizes attribute for responsive images. Here, Jason breaks down why that is (spoiler: it’s the lookahead pre-parser) and segues into a truly long term solution: a “magical” image format.

If you’ve ever thought it felt weird to put media conditions inside the HTML for responsive images, this will resonate.

A long-term plan for logical properties? | Miriam Eric Suzanne

Well, now I’m really glad I wrote that post about logical properties!

We’re not there yet. So how do we get there?

Well, I don’t know for sure – but articles like this are very helpful as we try to work it out!