CSS

CSS Gets Smarter: The New if() Function and reading-flow Property in Chrome 137

Today marks a major milestone for CSS developers. With the release of Chrome 137, the CSS if() function and reading-flow property are now available in production. These two features—seemingly simple—hold the potential to transform the way we write CSS, making it smarter, cleaner, and more adaptable.

Let’s break them down.

🔍 The `if()` Function: Conditional Logic in CSS

For years, we’ve relied on JavaScript or multiple CSS rules to achieve dynamic styling. Enter the if() function, a feature that brings conditional logic directly into CSS.

Here’s how it works:

font-size: if(var(--is-large) == 1, 2rem, 1rem);

This line tells the browser:

If the CSS custom property --is-large is 1, set the font-size to 2rem.
Otherwise, use 1rem.

Key Takeaways:

Powerful conditional styling without extra classes or JS.
Combines perfectly with var(), making your stylesheets more maintainable.
Supports complex expressions, such as if(calc(100% - var(--sidebar-width)) > 50%, ..., ...).
Improves responsiveness, dynamic theming, and fallback logic.

A caveat to note: Only modern browsers will support this, and while Chrome 137 leads the pack, other browsers may take time to catch up. Graceful degradation will be important for cross-browser compatibility.

🔍 The `reading-flow` Property: Control the Logical Flow

When working with languages and layouts that vary in direction—think vertical Japanese text, Arabic right-to-left, or even dynamic interfaces—the logical reading order is critical. That’s where the reading-flow property comes into play.

reading-flow: horizontal-tb; /* Default: horizontal, top-to-bottom */
reading-flow: vertical-rl;   /* Vertical, right-to-left */

With this, you’re explicitly telling the browser the logical flow of content, regardless of the physical layout. It’s a subtle yet powerful enhancement that:

Improves layout design for multi-directional scripts.
Enhances accessibility by aligning with screen readers and assistive technologies.
Gives authors more control over how content flows, especially in complex grid or flex layouts.
Future-proofs layouts for evolving design needs and internationalization.

🚀 Why These Features Matter

These features are not just “nice-to-haves.” They represent a shift in CSS philosophy—towards smarter, more dynamic stylesheets that can respond to conditions and respect reading logic across diverse scripts.

Here are some real-world benefits:

Conditional theming: Adapt themes based on user preferences or system states—directly in CSS.
Dynamic responsiveness: Adjust styles on the fly without bloating your markup with extra classes.
Internationalization-ready designs: Easily support multilingual, multi-directional content.
Cleaner codebases: Reduce reliance on JavaScript for style logic.

📌 A Few More Things to Consider

Before you rush to refactor all your CSS, keep in mind:

✅ Browser support: While Chrome 137 supports these features today, other browsers may take a few versions to catch up. Firefox and Safari might lag behind for a while. Feature detection and fallbacks will be essential.

✅ Performance considerations: Although if() logic is evaluated at parse-time or render-time, excessive nesting or overly complex expressions could impact render performance—especially on low-powered devices.

✅ Authoring complexity: With great power comes great responsibility. Avoid overcomplicating your CSS logic to the point where it’s harder to maintain than traditional approaches.

✅ Spec maturity: Both if() and reading-flow are new, and the specification details may still evolve. It’s a good idea to keep an eye on W3C updates and browser changelogs.

🌟 Finally: CSS Has Leveled Up

With the arrival of if() and reading-flow in Chrome 137, CSS has taken a bold step forward. These features empower developers to write more intelligent, adaptive, and accessible stylesheets, bringing logic and flow control into the language natively.

Mastering these tools early will give you an edge—whether you’re crafting responsive web apps, designing multilingual sites, or just trying to write cleaner CSS.

So, what’s your plan?
Will you be among the first to embrace these features and push the limits of CSS? 🚀

CSS Gets Smarter: The New if() Function and reading-flow Property in Chrome 137

🔍 The `if()` Function: Conditional Logic in CSS