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Supporting CSS Variables in Sass

I can’t say I’ve really been keeping up with the Sass scene. For personal projects, I’ve essentially stopped using it everywhere I can. Writing plain CSS files is much more friendly in the long game, as I can come back to a project in two years and not have to touch any build tools etc. and my CSS still works.

However, for larger projects, I can understand the need and I still use Sass for a couple employment-related projects. That’s how I ended up writing this blog post today.

First, some news (if you haven’t already heard): the default implementation of Sass is no longer going to be in Ruby, but in Dart (which compiles to JS):

Dart Sass has replaced Ruby Sass as the canonical implementation of the Sass language.

So what? Well, it means you don’t have to install node-sass anymore with all its extra bindings and gobbledygook stdout just to compile your Sass files (something even Dan worries about).

For the project I was working on, the implementation was pretty straightforward: remove node-sass devDependency, add sass devDependency, and change my build command for the CSS. However, I ran into a problem that took me a while to track down.

sass compiled my CSS just fine, but I also had postcss-cli processing my CSS with a couple plugins and it kept complaining about CssSyntaxError: ... missed semicolon. After troubleshooting for a while (running code through a linter, removing code, re-compiling, etc) I discovered the issue was where I was mapping some of my Sass variables to CSS custom properties (a.k.a CSS variables). Because I was on an older version of node-sass, I hadn’t noticed yet. node-sass continued to compile things just fine, but when I tried compiling the same files with sass, things were failing.

Turns out, when compiling with node-sass, this:

$color: #eee;
:root {
  --color: $color;
}

Compiles, as you would probably expect, to:

:root {
  --color: #eee;
}

However, using sass, that same thing would compile to:

:root {
  --color: $color;
}

Turns out, you have to interpolate your variable in this case so Sass can support CSS variables. So this:

$color: #eee;
:root {
  --color: #{$color};
}

Would result in your expected:

:root {
  --color: #eee;
}

This is by no means a ground-breaking revelation. Normally it’s not even worth a blog post. But I’m writing about it because when I was searching for the CssSyntaxError I was getting via the CLI, I wasn’t finding anything on the internet that helped solve my issue. So once I synthesized a couple disparate resources to solve the problem, I figured it’d be worth quickly noting down and posting on my blog, in case anyone out there on the internets has the same issue I did.