The read-only sheet property of the HTMLStyleElement interface contains the stylesheet associated with that element.
A StyleSheet is always associated with a HTMLStyleElement, unless its type attribute is not text/css.
A StyleSheet object, or null if none is associated with the element.
Suppose the <head> contains the following:
<style id="inline-style">
p {
color: blue;
}
</style>The sheet property of the associated HTMLStyleElement object will return the StyleSheet object describing it.
const style = document.getElementById("inline-style");
console.log(style.sheet.cssRules[0].cssText); // 'p { color: blue; }'