DocumentOrShadowRoot.styleSheets

The styleSheets read-only property of the DocumentOrShadowRoot interface returns a StyleSheetList of CSSStyleSheet objects, for stylesheets explicitly linked into or embedded in a document.

function getStyleSheet(unique_title) {
  for (var i=0; i<document.styleSheets.length; i++) {
    var sheet = document.styleSheets[i];
    if (sheet.title == unique_title) {
      return sheet;
    }
  }
}

The returned list is ordered as follows:

• StyleSheets retrieved from <link> headers are placed first, sorted in header order.
• StyleSheets retrieved from the DOM are placed after, sorted in tree order.