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How to easily configure your CSS variable colors

Since Tailwind CSS v3.1 we can include the opacity value with variable css without any effort.

We'd like to allow the user to choose his/her prefered color:

:root { --example-brand: "undefined" }

Following steps are required:

  1. Include css vars in your stylesheet
  2. Extend your tailwind.config.js file with the color
  3. Read and write the css var

If you'd like to jump directly into the code, here is the shortcut to:

or to my GitHub files:

1. Include css vars in your stylesheet

/* styles/global.css */
@tailwind base;
@tailwind components;
@tailwind utilities;

@layer base {
  :root {
    --example-brand: 255 0 0;
    /* ... */
  }
}

2. Extend your tailwind.config.js file with the color

// tailwind.config.js
module.exports = {
  theme: {
    colors: {
      brand: "rgb(var(--example-brand) / <alpha-value>)",
    },
  },
};

We can break it down in 3 important parts:

  • var(--example-brand) will access the css variable
  • <alpha-value> provides us a simple way to access the correct utility variable.
  • rgb(var / alpha) is a valid css color syntax where alpha is the opacityValue.

The way we extend the colors allows us to access the brand color on any utility class that tailwind provides: text-brand, border-brand,... and even change the opacity value e.g. bg-brand/10 (10%).

If you want to know how to include hsl values check out tailwinds documentation about "Using CSS variables".

3. Read and write the css var

Changing the color can happen with JavaScript via:

// write
const newValue = "0 255 0";
document.documentElement.style.setProperty("--example-brand", newValue);
// Example.tsx
<button className="... border-brand/10 bg-brand/5 text-brand/90">
  Look at me!
</button>

We can access the css variable on the client only one the page has been rendered with:

React.useEffect(() => {
  // read
  const style = getComputedStyle(document.body);
  const defaultValue = style.getPropertyValue("--example-brand");
}, []);

If you are interested in adding a color picker with the input type="color", you need to take aware that the target value is a hex value. You need to convert it to rgb.

To make the color consistent, you will need to store it either locally via localStorage/sessionStorage or on an external database.