use const

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

@@ -857,7 +857,7 @@ this.SingleFileCore = this.SingleFileCore || (() => {
 		async resolveLinkedStylesheetURLs() {
 			await Promise.all(Array.from(this.doc.querySelectorAll("link[rel*=stylesheet]")).map(async linkElement => {
 				const options = { maxResourceSize: this.options.maxResourceSize, maxResourceSizeEnabled: this.options.maxResourceSizeEnabled, charSet: this.charSet };
-				let stylesheetContent = await DomProcessorHelper.resolveLinkStylesheetURLs(linkElement.href, this.baseURI, options);
+				const stylesheetContent = await DomProcessorHelper.resolveLinkStylesheetURLs(linkElement.href, this.baseURI, options);
 				if (stylesheetContent && (!linkElement.rel.includes("alternate") || !linkElement.title)) {
 					const styleElement = this.doc.createElement("style");
 					if (linkElement.media) {