On December 19, 2023, Mozilla Firefox took a much needed step forward in web development and web development standardization by introducing support for the :has() CSS pseudo-class. Most other major browsers pushed out this feature between March 2022 and September 2022. This addition marks a major milestone in the quest for standardized web technologies, providing developers a powerful tool to streamline their styling processes and reduce dependence on JavaScript for certain styling tasks.

The :has() pseudo-class is a valuable addition to the CSS toolkit, enabling developers to select elements based on the presence of a specific selector within their descendants. This enhances the expressive power of CSS selectors, allowing for more nuanced and targeted styling, e.g., styling a div tag differently based on whether it has an img in it or a h1 in it.

With the :has() pseudo-class, developers can create more concise and efficient style rules. Previously, achieving similar effects often required JavaScript solutions, leading to increased code complexity and potential performance bottlenecks. Now, developers can achieve these goals directly within their stylesheets, promoting cleaner and more maintainable code. The example from below Mozilla showcases this best.

h1,
h2,
h3 {
  margin: 0 0 1rem 0;
}

:is(h1, h2, h3):has(+ :is(h2, h3, h4)) {
  margin: 0 0 0.25rem 0;
}

One of the most notable advantages of the :has() pseudo-class is its ability to reduce reliance on JavaScript for certain styling tasks. Traditionally, developers might have used JavaScript to manipulate the DOM and apply styles based on the presence of specific elements. With native CSS support for :has(), these operations can be done without the need for additional scripting, resulting in faster page rendering and a more efficient user experience.

The introduction of :has() enhances the readability of CSS code by allowing developers to express styling logic more directly within their stylesheets. This can lead to improved code maintainability, as developers can understand and modify styling rules more easily. Additionally, the reduction of JavaScript code for styling purposes contributes to a more easy-to-understand codebase and a better separation of styling and logic.

Standardization across browsers is crucial for ensuring a consistent user experience across different platforms. With Firefox joining other browsers in supporting the :has() pseudo-class, developers can confidently use this feature, knowing that it will be recognized by a broader audience. This promotes uniformity in web design regardless of their chosen browser.

Standardization encourages the adoption of new features across the web development community. As more browsers embrace common standards, developers are more likely to adopt these features in their projects. This creates a positive feedback loop, driving innovation and pushing the boundaries of what is possible in web design.

When browsers conform to standards, developers can allocate their time more efficiently, focusing on creating and optimizing content rather than dealing with browser-specific quirks. This ultimately leads to faster development cycles and reduced costs associated with cross-browser compatibility testing and bug fixing.