Profile the performance of your CSS selectors

  1. On the Profiles panel, select Collect CSS Selector Profile.
  2. To start profiling your memory usage, click Start. The button turns red as Web Inspector records the memory usage.
  3. To stop recording, click Stop. When you stop recording, the new profile is added under the CSS Selector Profiles section in the left pane and the profile's contents are displayed in the right pane:

    The profile results indicate the amount of time the browser engine spent matching each selector in the associated style sheets, along with the total number of times the browser engine found a match for the selector.
  4. To specify whether the value of the Total column is presented as a time value or as a percentage of the total time required to process the CSS, toggle the percent button on or off.