Marcin Wichary has written a great piece that dives into how he used CSS Variables to create a night mode and high contrast theme in an app. There’s so many neat tricks about how to use CSS Variables (Chris has also looked at theming) as well as how to organize them (Andras Galante has an interesting take on this) in here. Plus, Marcin shares some tricks about using filters to invert the color of an image.
I also also love this part of the article where Marcin writes:
I was kind of amazed that all of this could happen via CSS and CSS alone: the colours, the transitions, the vectors, and even the images...
CSS is mighty powerful these days, and it’s posts like Marcin’s that remind me it wasn’t that long ago that theming an app like this would’ve been impossible.
CSS preprocessor variables and CSS custom properties (often referred to as "CSS variables") can do some of the same things, but are not the same.
Practical advice from Mike Riethmuller:
If it is alright to use static variables inside components, when should we use custom properties? Converting existing preprocessor variables to custom properties usually makes little sense. After all, the reason for custom properties is completely different. Custom properties make sense when we have CSS properties that change relative to a condition in the DOM — especially a dynamic condition such as
:focus,:hover, media queries or with JavaScript.
We were all introduced to the env() function in CSS when all that drama about "The Notch" and the iPhone X was going down. The way that Apple landed on helping us move content away from those "unsafe" areas was to provide us essentially hard-coded variables to use:
padding:
env(safe-area-inset-top)
env(safe-area-inset-right)
env(safe-area-inset-bottom)
env(safe-area-inset-left);Uh ok! Weird! Now, nine months later, an "Unofficial Proposal Draft" for env() has landed. This is how specs work, as I understand it. Sometimes browser vendors push forward with stuff they need, and then it's standardized. It's not always waiting around for standards bodies to invent things and then browser vendors implementing those things.
I've been playing with CSS transforms for over five years and one thing that has always bugged me was that I couldn't animate the components of a transform chain individually. This article is going to explain the problem, the old workaround, the new magic Houdini solution and, finally, will offer you a feast of eye candy through better looking examples than those used to illustrate concepts.
I recently came across this Pen and my first thought was that it could all be done with just three elements: a wrapper, a range input and an output. On the CSS side, this involves using a conic-gradient() with a stop set to a CSS variable.
When I saw the original article on how to recreate this animation, my first thought was that it could all be simplified with the use of preprocessors and especialy CSS variables. So let's dive into it and see how!
Normally, the connection between CSS and HTML is that CSS selectors match HTML elements, and the CSS styles them. CSS doesn't know about the actual content in the HTML. But there is a way CSS can get its hands on data in HTML, so long as that data is within an attribute on that HTML element.
I came across a couple such animations a while ago and this gave me the idea of creating my own versions with as little code as possible, no external libraries, using various methods, some of which take advantage of more recent features we can use these days, such as CSS variables. This article is going to guide you through the process of building these demos.
One thing that single div pieces rarely do is animate. If you can transform your div or one of its pseudo elements, that's fair (as Lynn Fisher does with her fantastic BB-8). But you cannot directly change the opacity or transform of the individual "elements" you create inside your div, since they are not actual DOM elements.
I am a big believer of trying something a little different and interesting to learn tools you otherwise might never learn. Working with the constraints of a single div might not be great for production work, but it can be a great exercise (and challenge) to stretch your skills in a fun way. In that spirit, we'll use this technique to explore how Custom Properties (CSS Variables) work and even provide us a path to animation inside our div.