Impact of the Universal Selector on Performance

The universal selector (*) applies CSS styles to all elements in a document. While it was once considered detrimental to performance, advancements in modern browsers have mitigated its impact.

Equivalent Rules

The universal selector rule (* { margin: 0; padding: 0; }) is functionally equivalent to the more specific rule (body, h1, p { margin: 0; padding: 0; }). However, there are potential performance differences.

Browser Processing

Modern browsers typically use highly optimized style engines that efficiently process both universal and specific selectors. The universal selector may require slightly more processing initially to identify all elements, while specific selectors can directly apply styles to targeted elements.

Effects on Performance

The performance impact of the universal selector becomes more pronounced when applied to expensive effects. Special effects, such as box shadows or z-axis rotations, require more processing time. Using the universal selector to apply these effects to every element can slow down rendering.

Optimal Usage

For reset stylesheets or simple declarations that apply to all elements, the universal selector remains a valid and concise option. However, when performance is critical and expensive effects are involved, it's preferable to use specific selectors to target only the necessary elements.

Conclusion

In contemporary browsers, the performance impact of the universal selector is minimal. However, it's crucial to use it judiciously, especially with slow-effect CSS declarations, to avoid any potential performance pitfalls.