A layer is a kind of logical space that is interjected into the algorithm a CSS engine uses to determine what styles apply to elements based on cascading, specificity, and inheritance.

Custom elements in document heads can disrupt Google's rendering, potentially harming SEO; JSON-LD offers a flexible alternative. Using custom HTML tags in a web page's head can disrupt Google's ...

Google’s Search Relations team explains how CSS affects SEO, addressing myths about class names, pseudo elements, and page performance.