You can run Selenium automation tests on a scalable, secure, and reliable cloud-based Selenium grid. Perform automated cross-browser testing across many browsers and ensure that your users get a perfect experience across all browsers, browser versions, and operating systems.

This testing is independent of the deployment environments. Thus, it can be done in dev, test, QA or even production environments depending upon the availability of the application in each of these environments.

Also, each browser has its browser engine and they have their concept of displaying/rendering the Web content/pages, to test these we are performing testing on different browsers. So that making sure all the functionality and CSS are correct.