Here he is talking about custom properties in CSS as part of his Making Future Interfaces video series.
I think Cathy might’ve buried the lede:
The knock on effect of this was removing media queries. As I moved towards some of the more modern features of CSS the need to target specific screen sizes with unique code was removed.
But on the topic of Sass, layout is now taken care of with CSS grid, variables are taken care of with CSS custom properties, and mixins for typography are taken care of with
Personally, I’ve always found the most useful feature of Sass to simply be that you can have lots of separate Sass files that get combined into one CSS file—very handy for component libraries.
I had to read through this twice, but I think I get it now (I’m not the sharpest knife in the drawer). Very useful if you’re doing theming in CSS.
In defence of the cascade (especially now that we’ve got CSS custom properties).
I think embracing CSS’s cascade can be a great way to encourage consistency and simplicity in UIs. Rather than every new component being a free for all, it trains both designers and developers to think in terms of aligning with and re-using what they already have.
Remember, every time you set a property in CSS you are in fact overriding something (even if it’s just the default user agent styles). In other words, CSS code is mostly expressing exceptions to a default design.
On Ev’s blog, Marcin goes into great detail on theming an interface using CSS custom properties, SVG, HSL, and a smattering of CSS filters.
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.
This article is about using custom properties and CSS grid together, but I think my favourite part is this description of how custom properties differ from the kind of variables you get from a preprocessor:
let- they both serve different purposes.
Mike examines the real power of CSS custom properties compared to Sass variables—they can change at runtime.
I’m convinced that in almost all cases, responsive design logic should now be contained in variables. There is a strong argument too, that when changing any value, whether in a media query or an element scope, it belongs in a variable. If it changes, it is by definition a variable and this logic should be separated from design.
Harry demonstrates a really good use for CSS custom properties—allowing users to theme an interface.
Chris has a written a response to my post (which was itself inspired by his excellent An Event Apart presentation) all about CSS, variables, and abstractions.
I love this kind of old-school blog-to-blog discussion.