- CSS classes
- critical HTML classes
- critical resources
Explanation: To deliver the fastest possible time to first render, we need to minimize three variables:
- The number of critical resources.
- The critical path length.
- The number of critical bytes.
A critical resource is a resource that could block initial rendering of the page. The fewer of these resources, the less work for the browser, the CPU, and other resources.
Read more here: https://support.google.com/partners/answer/7336426