html

<p>I am displayed in <code>color: rebeccapurple</code>.</p>

css

@layer special {
  p {
    color: rebeccapurple;
  }
}

js

const item = document.getElementsByTagName("p")[0];
const rules = document.styleSheets[1].cssRules;
// Note that stylesheet #1 is the stylesheet associated with this embedded example,
// while stylesheet #0 is the stylesheet associated with the whole MDN page

const layer = rules[0]; // A CSSLayerBlockRule

item.textContent = `The CSSLayerBlockRule is for the "${layer.name}" layer`;