6 files declare their use of CssSelector in Zircon Profile 8

AssertContentTrait.php in core/modules/simpletest/src/AssertContentTrait.php

Contains \Drupal\simpletest\AssertContentTrait.

Crawler.php in vendor/symfony/dom-crawler/Crawler.php

CrawlerTest.php in vendor/symfony/dom-crawler/Tests/CrawlerTest.php

CssSelector.php in vendor/behat/mink/src/Selector/CssSelector.php

CssSelectorTest.php in vendor/symfony/css-selector/Tests/CssSelectorTest.php

FieldEntityTranslationTest.php in core/modules/views/src/Tests/Entity/FieldEntityTranslationTest.php

Contains \Drupal\views\Tests\Entity\FieldEntityTranslationTest.