CSS Preprocessor VS. Variables

Both CSS variables and preprocessor variables offer ways to manage styles and maintain code consistency, but with key differences:

Key Differences:

Native vs. Third-party

CSS Variables are integrated directly into the CSS language, supported by modern browsers without additional tools. In contrast, preprocessors like Sass or Less are external tools that enhance CSS functionality, requiring compilation into standard CSS before deployment.

Dynamic vs. Static

CSS Variables allow for real-time adjustments in the browser, empowering dynamic styling changes with JavaScript. Conversely, preprocessor variables are determined at compile-time, remaining static throughout runtime, limiting their adaptability to dynamic alterations.

Scoped vs. Global

CSS Variables are bound within the scope of their declaring elements or inherited contexts, facilitating modular and encapsulated styling. In contrast, preprocessor variables are global by default, accessible across the entire stylesheet, potentially leading to unintended side effects and reduced encapsulation.

Fallback Values

CSS Variables provide built-in support for fallback values, ensuring consistent rendering and degradation across browsers. Preprocessors lack native fallback mechanisms, necessitating manual implementation of fallback strategies to maintain compatibility and consistent styling across different environments.

CSS Variables

Native to CSS

CSS Variables, also known as Custom Properties, are native to CSS and are supported by modern browsers. They are declared using the -- prefix within a CSS rule.

:root { --primary-color: #007bff; }


CSS Variables are dynamic; their values can be changed dynamically using JavaScript, which makes them powerful for creating themes or implementing dark mode.

document.documentElement.style.setProperty('--primary-color', '#ff0000');


CSS Variables are scoped to the element they are declared in or inherited from. They follow the cascade, meaning you can override them at different levels of the DOM tree.

.container { --primary-color: #007bff; } .element { color: var(--primary-color); }

Fallback Values

You can define fallback values for CSS Variables, which will be used if the variable is invalid or unsupported.

.element { color: var(--primary-color, #007bff); }

Preprocessors (e.g., Sass or Less)

Not Native

Preprocessors like Sass or Less are not native to CSS; they are third-party tools that extend CSS with features like variables, nesting, and mixins. They need to be compiled into standard CSS before being deployed.

$primary-color: #007bff; .element { color: $primary-color; }


Preprocessor variables are static; their values are set at compile-time and cannot be changed dynamically in the browser.


Preprocessor variables are global by default. If you define a variable at the top level, its value is accessible throughout the stylesheet.

$primary-color: #007bff; .container { color: $primary-color; }

Mixins and Functions

Preprocessors often come with additional features like mixins and functions, which allow for more complex and reusable styles.

@mixin flex-center { display: flex; justify-content: center; align-items: center; } .container { @include flex-center; }

Let's say you want to create a theme-switching feature where users can switch between light and dark themes.

Using CSS Variables

:root { --primary-color: #007bff; --background-color: #ffffff; } .dark-theme { --primary-color: #ff0000; --background-color: #222222; } .element { color: var(--primary-color); background-color: var(--background-color); }

Using Sass:

$primary-color: #007bff; $background-color: #ffffff; .dark-theme { $primary-color: #ff0000; $background-color: #222222; } .element { color: $primary-color; background-color: $background-color; }

In this example, CSS Variables allow for dynamic theme switching directly in the browser, while with Sass, you would need to compile different versions of the stylesheet for each theme. Additionally, Sass provides features like mixins and functions, which can enhance code maintainability and reusability.

Choosing the right approach

For basic reuse and dynamic styles

Use CSS variables: CSS variables provide a simple and native solution for reusing values and enabling dynamic styling changes in the browser. They are ideal for scenarios where straightforward value management and runtime adjustments are sufficient for achieving desired styling outcomes efficiently.

For complex features, mixins, and future-proofing

Consider a preprocessor: Preprocessors like Sass or Less offer a wealth of advanced features such as mixins, functions, and nesting, enabling the creation of complex stylesheets with enhanced maintainability and readability. They are well-suited for projects requiring sophisticated styling logic and a future-proof approach to code management.

Evaluate trade-offs

When deciding between CSS variables and preprocessors, consider the trade-offs involved. CSS variables provide dynamic flexibility directly in the browser, simplifying development but offering limited functionalities. Preprocessors offer extensive features but require compilation, adding complexity to the development workflow and potentially increasing maintenance overhead. Choose based on project requirements and development priorities.


CSS Variables are native to CSS, allowing for dynamic styling changes directly in the browser and scoped to their declaring elements. Preprocessors like Sass or Less are third-party tools that offer advanced features such as mixins and functions, but require compilation, making them more suitable for complex styling needs and global variable management.