What Is the CSS if() Function
The CSS if() function represents a fundamental shift in how developers can express conditional logic within stylesheets. Rather than relying on separate @media blocks, @supports rules, or JavaScript-driven class changes, the if() function allows conditional expressions directly within property values.
Unlike traditional CSS conditionals that operate at the rule block level, the if() function operates within individual property declarations. This means you can have multiple conditions evaluated independently within the same rule, with different properties responding to different conditions simultaneously.
Web development has long required workarounds to apply conditional styles. The if() function changes this paradigm by bringing native conditional logic directly into CSS property values, enabling developers to write responsive web design that is more maintainable, more readable, and more powerful than ever before, according to Chrome for Developers.
Syntax and Fundamentals
The if() function follows a specific syntax pattern: property: if(condition1: value1; condition2: value2; else: fallback);
Key syntax requirements:
- No space between "if" and the opening parenthesis
- Each condition separated from its value with a colon
- Condition-value pairs separated with semicolons
Simple Example
button {
width: if(media(pointer: coarse): 44px; else: 30px);
}
This adapts button size based on the user's pointer device--touchscreen gets 44px, mouse gets 30px. The conditions are evaluated in order, and the first matching condition returns its associated value. This "short-circuit" behavior is important for performance and for understanding how multiple conditions interact.
For developers building modern web applications, this inline approach keeps all conditional logic self-contained within each property declaration.
Style queries enable conditional styling based on CSS custom properties on the element:
color: if(style(--theme: dark): #eeeeee; style(--theme: light): #333333; else: #000000);
border-color: if(style(--status: complete): seagreen; style(--status: pending): royalblue; else: gray);
Use for: Theming, state-based styling, design system conditional values. Style queries query the element being styled directly, making them more efficient than container style queries for element-level conditions.
Practical Applications
Responsive Component Design
Create truly responsive components with inline conditionals. This approach keeps all responsive logic within the component's rule block, making it easier to understand and maintain than scattering media queries throughout the stylesheet:
.card {
padding: if(media(width > 600px): 1.5rem; else: 1rem);
font-size: if(media(width > 600px): 1rem; else: 0.875rem);
gap: if(media(width > 600px): 1.5rem; else: 1rem);
}
Multi-State Theming
Build design systems with multiple themes without creating separate classes for each theme:
:root {
--theme: ocean;
--ocean-bg: #e0f7fa;
--forest-bg: #e8f5e9;
}
body {
background: if(
style(--theme: ocean): var(--ocean-bg);
style(--theme: forest): var(--forest-bg);
else: #ffffff
);
}
This pattern scales to any number of themes, with each theme adding a condition-value pair. The theme is changed by updating a single custom property value.
Combining with Other Functions
/* Theme + light-dark combination */
--bg: if(
style(--theme: dark): light-dark(var(--dark-bg), var(--light-bg));
style(--theme: light): light-dark(var(--light-bg), var(--dark-bg))
);
/* Conditional calculations with calc() */
--scale: if(media(width > 1000px): 1.5; media(width > 600px): 1.25; else: 1);
transform: scale(calc(var(--scale) * 1.2));
Using @property to register custom properties with explicit syntax enables the browser to properly evaluate computed values within if() conditions.
Teams implementing AI-powered automation in their workflows can leverage these CSS techniques to build more adaptive and maintainable user interfaces.
Always Include else Clause
Provide fallback values for unsupported browsers or unmatched conditions to ensure predictable styling. Without else, unmatched conditions return a guaranteed-invalid value.
Order Conditions Strategically
Place more likely conditions first for better performance and fewer evaluations. Conditions are evaluated sequentially until a match is found.
Use @property for Type Safety
Register custom properties with explicit syntax to enable reliable condition evaluation. This ensures computed values are properly handled in calculations.
Leverage Custom Properties
Define complex conditions as custom properties for cleaner, more maintainable if() declarations. This separates condition definition from application.
Browser Support and Considerations
Current Support Status
- Chrome 137+: Fully supported
- Edge 137+: Fully supported (Chromium-based)
- Firefox: Behind experimental flags
- Safari: No support yet
The function is not yet part of Baseline, meaning it cannot be relied upon for universal support. Developers should use feature detection when adopting the feature in production.
Progressive Enhancement Pattern
For production use, the recommended approach is progressive enhancement--use if() to enhance experiences for supported browsers while ensuring acceptable experiences for unsupported browsers:
.element {
/* Enhancement for supported browsers */
width: if(supports(width: calc(1px)): 100%; else: auto);
}
The conditional itself provides the enhancement, while the fallback ensures usable experiences for all users. For critical styling that requires if() for correct behavior, consider feature-detection-based loading of alternate stylesheets.
As browser support expands, adoption will likely increase, particularly for design systems and component libraries that can leverage the feature for more maintainable stylesheets.
Related Resources
Explore more web development guides for additional CSS techniques and modern development practices.