CSS variables (also called custom properties) are a feature in Cascading Style Sheets that let you store reusable values — like colors, font sizes, or spacing — in one place and reference them throughout your stylesheet. Instead of repeating the same value over and over, you define a variable once using -- syntax (like --main-color: #333;) and use it anywhere with var(--main-color). This makes your styles easier to update, maintain, and scale.

They're especially helpful when designing consistent themes across a website or when building modern, flexible layouts with an AI website builder. Even though CSS variables work differently from preprocessor variables like in Sass, they're dynamic, meaning you can change them with JavaScript or within different elements and media queries for responsive design.

How CSS variables work

You define CSS variables inside a selector (typically the :root pseudo-class if you're applying them globally), and then call them where needed. For example:

css

CopyEdit

:root {

  --primary-color: #0077ff;

  --font-size-large: 1.5rem;

}

`h1 {`

`  color: var(--primary-color);`

`  font-size: var(--font-size-large);`

`}`

``

``

``

This keeps your styles consistent and centralized, so you only need to make updates in one place when design tweaks are needed.

## Why use CSS variables in modern web design?

If you're building a scalable site or managing multiple themes, CSS variables save time and reduce errors. They’re particularly useful in design systems and when collaborating across teams. Plus, since they’re native to CSS, there’s no need for additional build tools or preprocessing.

For professionals using platforms like [B12](https://www.b12.io/), CSS variables offer another level of control for branding and styling without bloated code or rigid design constraints.

## Benefits of CSS variables

* Consistency: Reuse values to maintain visual harmony.
* Maintainability: Update one value instead of hunting through stylesheets.
* Theming: Easily swap themes or apply dark/light modes.
* Responsiveness: Adjust values with media queries or JavaScript.
* Cleaner code: Reduce duplication and hard-coded values.

## Common use cases

* Setting up color palettes for dark/light themes
* Adjusting layouts dynamically with media queries
* Creating flexible, consistent typography and spacing scales
* Customizing user dashboards or client-facing interfaces for better [client engagement](https://www.b12.io/client-engagement/)

## FAQs about CSS variables

### Can I use CSS variables in all browsers?

Most modern browsers support CSS variables, including Chrome, Firefox, Edge, and Safari. However, older versions of Internet Explorer do not support them, so fallback styles may be needed if you need legacy compatibility.

### How are CSS variables different from Sass or Less variables?

CSS variables are native to the browser and can change dynamically in the DOM. Sass or Less variables are compiled at build time and can't change after that. CSS variables also allow scoping, which preprocessor variables don’t.

### Can I update a CSS variable using JavaScript?

Yes! You can modify CSS variables dynamically with JavaScript by targeting the element and using `.style.setProperty('--your-variable', 'new-value').`

### Do CSS variables affect performance?

Used properly, CSS variables can improve performance by reducing duplication and simplifying code. However, excessive or deeply nested usage could slightly affect rendering performance in very large apps.

### Are CSS variables secure?

CSS variables are as secure as any other front-end code. They don’t expose sensitive data — just style values — and work like traditional CSS from a security perspective.

## How CSS variables help designers and developers stay consistent

Using CSS variables isn’t just a best practice — it’s a smart, scalable way to manage the look and feel of your website. Whether you're tweaking fonts or applying brand colors, having one place to manage your styles saves time and reduces stress. If you're using tools like [B12 AI Assist](https://www.b12.io/ai-assist/) for content creation or combining design work with tools like [email marketing](https://www.b12.io/email-marketing/) and [online scheduling](https://www.b12.io/bookings-scheduling-software/), CSS variables help maintain a polished, professional appearance with less hassle.

Try using them in your next project or let a smart platform like [B12](https://www.b12.io/) handle it all for you. [Get started](https://b12.io/signup) today to explore how simple, flexible, and efficient web design can be.



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