CSS{In Real Life}

Heatwave: An Animated CSS Sun Illustration

Animated sun illustration

We’re right in the middle of a heatwave here in the UK, and things have been a little quiet on this blog while I’ve been very busy with various other projects. So I’d thought I’d take a little break today and try something a little bit fun – an animated CSS sun illustration, to capture the summer spirit (and the relentless heat)!

Initially I started layering divs, but then I realised I could create the whole thing with just a single element, using background gradients! The first (static) version was quite simple – I didn’t even need any pseudo elements (fig 01).

Simple sun illustration
Fig 01 The first iteration

But it felt quite basic. I wanted to give the sun’s rays a bit more life, and add some animation. So I added two pseudo elements (::before and ::after).

Layered gradients

The two pseudo elements, and the element itself, all have mutliple layered background gradients. These use radial-gradient for the glow, and conic-gradient for the rays. conic-gradient has mixed browser support at the time of writing, so the demo can only be viewed in Chrome or Safari – you won’t see anything in Firefox. Although Firefox supports radial-gradient, because we’re using it in combination with conic-gradient the whole declaration is dropped.

I gave the main body of the sun a slightly fuzzy edge by adding a few pixels between the orange colour stop and the transparent region – I didn’t want it to feel too sharp and solid:

.sun::after {
	background: radial-gradient(
		yellow,
		orange 27%,
		transparent calc(27% + 3px) 100%
	);
}

Z-index and backgrounds

I ran into a bit of a z-index issue when layering my gradients – ideally I wanted the body of the sun to be on the main element and the pseudo elements to only contain the sun’s rays, so that I could animate them independently. But I couldn’t get the z-indexes to play nicely. It seems the background of the element is always going to be behind the pseudo elements, no matter what, which kind of makes sense – although if this is incorrect please let me know!

I could have easily got around this by nesting an element, but I wanted to keep the purity of the single-element solution! In the end I decided not to scale the second set of rays anyway, but having the option would be useful (without resorting to anything too complex).

Mask-image

To give the rays a soft edge I used mask-image with a radial gradient over the element. Image masking is similar to clip-path in that it is a way to show or hide part of an element. But instead of providing a path to cut out the shape, it’s more like drawing over the areas you want to show. You can use a PNG, SVG or gradient to mask, for example.

mask-image requires a prefix for some browsers (including Chrome):

.sun {
	-webkit-mask-image: radial-gradient(rgba(0, 0, 0, 1) 40%, transparent 65%);
	mask-image: radial-gradient(rgba(0, 0, 0, 1) 40%, transparent 65%);
}

Because I’m animating the scale of the rays I duplicated this property onto the pseudo element too, so that the same proportion would remain hidden as it scales.

Animation

I animated the two pseudo elements so they rotated at different rates. This wasn’t quite enough, so I animated the scale of one of them too, to give the impression of a pulsating glow.

Here’s the full demo: