CSS was once a purely presentational language. It imperatively handled fonts, colors, backgrounds, spacing, layouts, and other styles for markup languages. It was a language for appearance, doing what it was asked, never thinking or making decisions. At least, that is what it was created for when Håkon Wium Lie proposed CSS in 1994, and the World Wide Web Consortium (W3C) adopted it two years later.
Fast-forward to today — a lot has changed with the addition of new features, and even more are on the way, moving the styling language toward a more imperative paradigm. CSS now actively supports complex responsive and interactive user interfaces. With recent advances such as container queries, relational pseudo-classes, and the if() function, the language that once lived in the presentation layer has entered logic territory, reducing its dependence on the language that has traditionally handled its logical side: JavaScript.
This shift raises interesting questions about CSS and its future for developers. CSS deliberately stayed in the styling space for a long time, but is it time for that to change? Also, is CSS still a presentational language, as it was in the beginning, or is it becoming something more and larger? This article explores how smart CSS has become over the years, where it is heading, what problems it solves, whether it is becoming too complex, and how developers are responding to this shift.
Historical context: CSS’s intentional simplicity
A look at the history of CSS shows a language born to separate content from presentation, making web pages easier to manage and maintain. The first official version of CSS, CSS1, was released in 1996 and introduced basic styling capabilities such as font properties, colors, the box model (padding, margin, and border), dimensions (width and height), a few simple display types (none, block, and inline), and basic selectors.
Two years later, CSS2 was released, expanding what CSS could style in HTML by adding features such as positioning, z-index, improved selectors, table layouts, and media types for different devices. However, the styling language had inconsistencies — a problem CSS2.1 addressed in 2011, becoming the foundation of modern CSS. This simplified web development and website maintenance.
Between CSS1 and CSS2.1, CSS was largely static and declarative. Developers experienced both frustrations and breakthroughs in their projects. Because intuitive layout tools such as Flexbox and CSS Grid did not yet exist, developers relied on hacky alternatives using table layouts, positioning, or floats to implement complex designs, even though floats were originally intended to let text wrap around an obstacle on a web page, usually a media object. As a result, developers ran into issues such as collapsing containers and unexpected element placement. Despite that, basic styling was intuitive. A beginner could start learning web development today and add basic styles the next day. CSS was separated from content and logic, making it highly performant and lightweight.
CSS3: The first step toward context awareness
Everything changed with the release of CSS3. Developers expected a single monolithic update, as with previous versions, but their expectations and the reality of the latest release did not match. CSS3 rolled out a modular system with powerful layout tools such as Flexbox, CSS Grid, and media queries, defining for the first time how developers build responsive designs. With more than 20 modules, CSS3 marked the beginning of “smarter CSS.”
The introduction of Flexbox around 2012 provided a flexible one-dimensional layout system, while CSS Grid’s 2017 launch took layout even further by offering a two-dimensional layout system that allows complex designs with minimal code. These advances, as discussed by Chris Coyier, reduced reliance on hacks such as floats.
That is not all. There are media queries, a standout CSS3 release and one of the main building blocks of this smart CSS. With media queries, CSS can respond to different device screens, adapting its styles to screen dimensions, aspect ratio, and orientation — something earlier versions could not easily accomplish. At level five, it added user preference media features, such as prefers-color-scheme and prefers-reduced-motion, making CSS more user-centered by adapting styles to user settings and improving accessibility.
CSS3 marked the beginning of context-aware CSS.
Context awareness is the ability to understand and respond accordingly to the situation around you or in your environment. It means systems and devices can sense critical information, such as your location, the time of day, and your activity, and adapt accordingly.
In web development, the term “context awareness” has always been used in relation to components, but what makes a component context-aware? If you mentioned anything other than the component’s styles, you were wrong! For a component to be considered context-aware, it must sense the presence of its environment and know what is happening in it. For example, for your website to update its styles to support dark mode, it must know about the user’s preferences. Similarly, to change its layout, the website must know which device the user is accessing it from — and thanks to user preference media queries, that is possible.
Despite these features, CSS remained largely reactive. It responded to external factors such as screen size (through media queries) or input states (such as :hover, :focus, or :checked), but it never made decisions based on changes in its own environment. For that level of interactivity, developers usually turned to JavaScript.
But not anymore.
For example, with container queries and, more recently, container style queries, CSS now responds not only to layout constraints but also to design intent. It can adapt based on a component’s environment and even its parent’s theme or state. And that is not all. The recently specified if() function promises inline conditional logic, allowing styles to change depending on conditions, all without scripts.
These changes show CSS moving from presentation toward behavior management, challenging its traditional role.
New CSS features driving intelligence
Several features are currently pushing CSS toward a dynamic and adaptive edge, making it smarter, but these two are especially worth mentioning: container style queries and the if() function.
What are container style queries and why do they matter?
To better understand what container style queries are, it makes sense to pause briefly on their close relative: container size queries, introduced in CSS Containment Module Level 3.
Container size queries allow developers to style elements based on the dimensions of their parent container. This is a huge win for component-based designs, because it removes the need to squeeze responsive styles into global media queries.
/* Size-based container query */
@container (min-width: 500px) {
.card {
flex-direction: row;
}
}Container style queries go even further by letting you style elements based on custom properties, also known as CSS variables, set on the container.
/* Style-based container query */
@container style(--theme: dark) {
.button {
background: black;
color: white;
}
}These features are a big deal for CSS because they unlock the possibility of context-aware components. A button can change its appearance based on a --theme property set by its parent element, without JavaScript or hard-coded classes.
The if() function: a glimpse into the future
The CSS if() function may be the most radical shift. Once it is implemented — Chrome is the only browser that supports it, as of version 137 — it will allow developers to write inline conditional logic directly in property declarations. Think of a ternary operator in CSS.
padding: if(style(--theme: dark): 2rem; else: 3rem);This hypothetical line or pseudocode, not syntax, sets the text color to white if the --theme variable equals dark, or black otherwise. Currently, the if() function is not supported in any browsers, but it is on the CSS Working Group’s radar, and influential developers such as Lea Verou are already exploring its possibilities.
The new CSS: is the line between CSS and JavaScript disappearing?
Traditionally, the division of responsibilities around styling was this: CSS is how things look, while JavaScript is how things work. But features such as container style queries and the specified if() function are beginning to blur that line. CSS is starting to behave — not in the sense of API calls or event listeners, but in its ability to conditionally apply styles based on logic or context.
As web development has evolved, CSS has started moving into JavaScript territory. CSS3 brought animations and transitions — a powerful combination for interactive web development that previously was not possible without JavaScript. Today, research shows that CSS has taken over several interactive tasks that JavaScript once handled. For example, the :hover pseudo-class and the transition property allow visual feedback and smooth animations, as discussed in “Bringing Interactivity to Your Website With Web Standards.”
That is not all. Toggling accordions and modals used to belong to JavaScript, but today it is possible with new powerful CSS combinations such as the <details> and <summary> HTML tags for accordions, or modals using the :target pseudo-class. CSS can also handle tooltips using aria-label with content: attr(aria-label), and star ratings with radio buttons and labels, as detailed in the same article.
Another article, “5 Things You Can Do With CSS Instead of JavaScript,” lists features such as scroll-behavior: smooth for smooth scrolling and @media (prefers-color-scheme: dark) for dark mode — tasks that once required JavaScript. In the same article, you can also see that it is possible to build a carousel without JavaScript using CSS scroll snapping (and we are not even talking about features specifically designed for creating CSS-only carousels, which were recently prototyped in Chrome).
These CSS expansions into JavaScript’s territory now leave JavaScript mostly responsible for complex, essential interactions in a web application, such as user input, API calls, and state management. Although CSS pseudo-classes such as :valid and :invalid can help as error or success indicators on input elements, you still need JavaScript for dynamic content updates, form validation, and real-time data fetching.
CSS is now solving problems many developers did not even know they had. By removing JavaScript from many style-related scenarios, developers now have simplified codebases. There are fewer dependencies, less overhead, and better website performance, especially on mobile devices. In fact, this shift brings CSS closer to a more accessible web, because CSS-based designs are often easier for browsers and assistive technologies to process.
Although new features bring many benefits, they also introduce complexities that did not previously exist:
- What happens when logic is distributed across both CSS and JavaScript?
- How do you debug conditional styles without a clear view of what triggered them?
- CSS used to handle only basic styling, such as colors, fonts, layouts, and spacing, which was easier for new developers to learn. How much more difficult does the learning curve become when these new features require understanding concepts that once belonged exclusively to JavaScript?
Developers are divided. While some welcome the idea of a natural evolution toward a smarter, more component-focused web, others worry that CSS is becoming too complex — a language originally designed for formatting documents now juggling logic trees and style calculations.
A divided opinion: is logic in CSS helpful or harmful?
Although the evidence in the previous section points toward a blurring of boundaries, there is significant disagreement among developers. Many modern developers argue that logic in CSS has long been needed. As components have become more important in web development, the limits of declarative styling have become more obvious, so supporters see logic as a necessary evolution for what was once a purely styling language.
For example, in frontend libraries such as React, components often need conditional styles based on props or state. Developers have had to make do with JavaScript or CSS-in-JS solutions in these cases, but the truth is that these solutions are not ideal. They introduce complexity and tie styles to logic. CSS and JavaScript should have separate responsibilities in web development, but libraries such as CSS-in-JS ignored the rules and merged the two.
We have seen how preprocessors such as SASS and LESS proved the usefulness of conditions, loops, and variables in styling. Developers who do not embrace the CSS-in-JavaScript approach have settled for these preprocessors. Nevertheless, like Adam Argyle, they have expressed the need for native CSS solutions. With native conditions, developers could reduce JavaScript overhead and avoid runtime class toggling to achieve conditional rendering.
“It never felt right to me to manipulate styling settings in JavaScript when CSS is the right tool for the job. With CSS custom properties, we can send into CSS what needs to come from JavaScript.”
— Chris Heilmann
Similarly, Bob Ziroll dislikes using JavaScript for what CSS is meant to do, and considers it unnecessary. This reflects a preference for using CSS for styling tasks, even when JavaScript is involved. These developers embrace new CSS capabilities, seeing them as a way to reduce dependence on JavaScript for performance reasons.
Others argue against it. Introducing logic into CSS is a slippery slope, and CSS may lose its core strengths — simplicity, readability, and accessibility — by becoming too much like a programming language. The fear is that developers risk making the web more complicated than it needs to be.
“I’m old school. I like my CSS separated from my HTML; my HTML separated from my JS; my JS separated from my CSS.”
— Sara Soueidan
This view emphasizes the traditional separation of concerns, arguing that mixing roles can make maintenance harder. Brad Frost has also expressed skepticism, specifically about CSS-in-JS, saying that it “doesn’t port to non-JS framework environments, adds more noise to an already-noisy JS file, and the demos I saw weren’t reflective of CSS best practices.” This highlights concerns about scalability and best practices, showing that a disappearing boundary may not always be beneficial.
Community discussions, such as those on Stack Overflow, also reflect this divide. A question such as “Is it always better to use CSS when possible instead of JS?” gets answers supporting CSS for performance and simplicity, while others argue that JavaScript is necessary for complex scenarios, illustrating the ongoing debate. Do not be fooled. It may seem convenient to agree that CSS performs better than JavaScript for styling, but that is not always the case.
Smarter CSS without losing its soul
CSS has always stood apart from full programming languages such as JavaScript by being declarative, accessible, and purpose-driven.
If CSS is to become smarter, the challenge is not to make it more powerful for its own sake, but to let it evolve without damaging its core purpose.
So what might logically enriched but still declarative CSS look like? Let’s find out.
Conditional rules (if(), @when…@else) with carefully introduced logic
An important area of CSS evolution is the introduction of native conditions through the if() function and @when…@else rules, which are part of the CSS Conditional Rules Module Level 5 specification. Although still in the early draft stage, these would allow developers to apply styles based on evaluated conditions without turning to JavaScript or a preprocessor. Unlike the imperative nature of JavaScript, these conditions aim to keep logic integrated into the existing CSS flow, aligned with the cascade and specificity.
More powerful, more precise selectors
Selectors have always been one of CSS’s core strengths, and expanding them in a targeted way would make it easier to express relationships and conditions declaratively without needing classes or scripts. Currently, :has() allows developers to style a parent element based on a child, while :nth-child(An+B [of S]?) (Selectors Level 4) enables more complex matching patterns. Together, they allow greater precision without changing the nature of CSS.
Localized styling without JavaScript
One of the challenges developers face in component-based frameworks such as React or Vue is style localization. Style localization ensures that styles apply only to specific elements or components and do not “leak” outward. Previously, achieving this required implementing BEM naming conventions, CSS-in-JS, or build tools such as CSS Modules. Native localized styling in CSS, through the new experimental @scope rule, allows developers to wrap styles in a specific context without extra tools. This feature makes CSS more modular without tying it to JavaScript logic or complex class systems.
Now the fundamental design question is whether we can give CSS more power without making it feel like JavaScript. The truth is that giving CSS conditional logic, powerful selectors, and localized rules does not require it to copy JavaScript’s syntax or complexity. The goal is declarative expressiveness, giving CSS more awareness and control while preserving its clear, readable nature — and that is where we should focus. Done correctly, smarter CSS can strengthen the language’s strengths rather than weaken them.
The real danger is not logic itself, but uncontrolled complexity that buries the simplicity CSS was created with.
Warnings and limitations: why smarter is not always better
The push toward smarter CSS brings significant trade-offs alongside control and flexibility. Over the years, history has shown that adding a new feature to a language, framework, or library usually introduces complexity, not only for beginners but also for expert developers. The danger lies not in CSS gaining power, but in how that power is implemented, taught, and used.
One of CSS’s greatest strengths has always been its beginner-friendly simplicity. Designers and beginners could quickly learn the basics: selectors, properties, and values. With more logic, scoping, and advanced selectors, that learning curve becomes steeper. The risk is a growing gap between “basic CSS” and “real-world CSS,” echoing what happened with JavaScript and its ecosystem.
As CSS becomes more powerful, developers increasingly rely on tools to manage and abstract that power, such as build systems (for example, webpack and Vite), linters and formatters, and component libraries with strict styling conventions. This creates dependencies that are hard to avoid. Tooling becomes a prerequisite rather than a choice, further complicating onboarding and increasing setup time for projects that once worked with a single stylesheet.
Also, more logic means more potential for unexpected results. New problems may arise that are harder to spot and fix. Resources such as DevTools will need to evolve to visualize scope boundaries, conditional applications, and complex selector chains. Until then, debugging may remain a challenge. All of these problems are experienced with CSS-in-JS; how much more with native CSS?
We have seen this before. CSS history is full of overly complicated solutions, such as tables for layout before Flexbox, reliance on floats with clearfix hacks, and overly rigid grid systems before native CSS Grid. In each case, the hacky solution eventually became the problem. CSS improved not by imitating other languages, but by standardizing thoughtful, declarative solutions. With the right powers, in the end, we can make CSS better.
Conclusion
We have just walked through the paths of CSS history, examined its present, and looked at what its future might become. We can all agree that CSS has come a long way from a simple, declarative language to a dynamic, context-aware, and yes, smarter language. Of course, evolution brings tension: a smarter styling language with fewer dependencies on scripts, and a complex language with a steeper learning curve.
Here is the conclusion we draw:
CSS’s future should not be a race to add logic for the sake of logic. Instead, it should be a thoughtful expansion, balancing power with clarity and grounding innovation in accessibility.
That means asking difficult questions before releasing new features. It means ensuring that new capabilities help
