Performance Hands-On: CSS Selector Performance

How to Use This Demo

Open Chrome DevTools (F12 or Ctrl+Shift+I)
Go to the Performance panel
Click the Record button (or press Ctrl+E)
Click the buttons below to trigger different CSS selector evaluations
Stop the recording and analyze the results
Look for "Recalculate Style" events in the flame chart
Click on these events to see detailed CSS selector performance metrics
Look at the "Selector stats" next to the Summary tab at the buttom

Key Insight: The browser has to work harder with complex CSS selectors, which can impact performance.

CSS Selector Performance Demo

Understanding Performance Panel Results

Column	What It Means
Elapsed (ms)	Time spent matching this selector - lower is better!
Match Attempts	Elements the browser tried to match with this selector
Match Count	Elements that actually matched the selector
Selector	The CSS selector being evaluated

Best Practices for CSS Selector Performance

Use ID selectors when possible (#element) - fastest
Use class selectors (.myclass) - very efficient
Avoid deep nesting (.grand > .parent > .child > element)
Limit universal selectors (* or *:not())
Be cautious with attribute selectors ([attr=value])
Avoid complex pseudo-selectors (:nth-child(n+5):not(:last-child))