Add support of escaped URLs in CSS

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

@@ -888,7 +888,7 @@ this.singlefile.lib.core = this.singlefile.lib.core || (() => {
 				if (this.options.compressCSS) {
 					styleContent = util.compressCSS(styleContent);
 				}
-				styleContent = ProcessorHelper.resolveStylesheetURLs(styleContent, this.baseURI);
+				styleContent = ProcessorHelper.resolveStylesheetURLs(styleContent, this.baseURI, this.workStyleElement);
 				const declarationList = cssTree.parse(styleContent, { context: "declarationList" });
 				this.styles.set(element, declarationList);
 			});
@@ -1547,7 +1547,7 @@ this.singlefile.lib.core = this.singlefile.lib.core || (() => {
 		}
 
 		static async resolveImportURLs(stylesheetContent, baseURI, options, workStylesheet, importedStyleSheets = new Set()) {
-			stylesheetContent = ProcessorHelper.resolveStylesheetURLs(stylesheetContent, baseURI);
+			stylesheetContent = ProcessorHelper.resolveStylesheetURLs(stylesheetContent, baseURI, workStylesheet);
 			const imports = getImportFunctions(stylesheetContent);
 			await Promise.all(imports.map(async cssImport => {
 				const match = matchImport(cssImport);
@@ -1596,11 +1596,15 @@ this.singlefile.lib.core = this.singlefile.lib.core || (() => {
 			return stylesheetContent;
 		}
 
-		static resolveStylesheetURLs(stylesheetContent, baseURI) {
+		static resolveStylesheetURLs(stylesheetContent, baseURI, workStylesheet) {
 			const urlFunctions = getUrlFunctions(stylesheetContent, true);
 			urlFunctions.map(urlFunction => {
 				const originalResourceURL = matchURL(urlFunction);
-				const resourceURL = normalizeURL(originalResourceURL);
+				let resourceURL = normalizeURL(originalResourceURL);
+				workStylesheet.textContent = "tmp { content:\"" + resourceURL + "\"}";
+				if (workStylesheet.sheet && workStylesheet.sheet.cssRules) {
+					resourceURL = util.removeQuotes(workStylesheet.sheet.cssRules[0].style.getPropertyValue("content"));
+				}
 				if (!testIgnoredPath(resourceURL)) {
 					if (!resourceURL || testValidPath(resourceURL)) {
 						let resolvedURL;