move down the style elemnt used to store variables

lib/single-file/single-file-core.js

@@ -810,11 +810,7 @@ this.SingleFileCore = this.SingleFileCore || (() => {
 				if (firstStyleElement) {
 					this.doc.head.insertBefore(styleElement, firstStyleElement);
 				} else {
-					if (this.doc.head.firstChild) {
-						this.doc.head.insertBefore(styleElement, this.doc.head.firstChild);
-					} else {
-						this.doc.head.appendChild(styleElement);
-					}
+					this.doc.head.appendChild(styleElement);
 				}
 				let stylesheetContent = "";
 				this.cssVariables.forEach((content, indexResource) => {