added support of nested functions when parsing CSS declaration values

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

@@ -1301,26 +1301,31 @@ this.SingleFileCore = this.SingleFileCore || (() => {
 								let { content, indexResource, duplicate } = await batchRequest.addURL(resourceURL);
 								if (duplicate && options.groupDuplicateImages) {
 									const tokens = [];
-									for (let token = declaration.value.children.head; token; token = token.next) {
-										if (token.data.type == "Url" && DOM.removeQuotes(DomUtil.getCSSValue(token.data.value)) == originalResourceURL) {
-											const value = cssTree.parse("var(" + SINGLE_FILE_VARIABLE_NAME_PREFIX + indexResource + ")", { context: "value" }).children.head;
-											tokens.push({ token, value });
-										}
-									}
-									tokens.forEach(({ token, value }) => declaration.value.children.replace(token, value));
+									findURLToken(originalResourceURL, declaration.value.children, (token, parent) => {
+										const value = cssTree.parse("var(" + SINGLE_FILE_VARIABLE_NAME_PREFIX + indexResource + ")", { context: "value" }).children.head;
+										tokens.push({ parent, token, value });
+									});
 									cssVariables.set(indexResource, content);
+									tokens.forEach(({ parent, token, value }) => parent.replace(token, value));
 								} else {
-									declaration.value.children.forEach(token => {
-										if (token.type == "Url" && DOM.removeQuotes(DomUtil.getCSSValue(token.value)) == originalResourceURL) {
-											token.value.value = content;
-										}
-									});
+									findURLToken(originalResourceURL, declaration.value.children, token => token.data.value.value = content);
 								}
 							}
 						}
 					}));
 				}
 			}));
+
+			function findURLToken(url, children, callback) {
+				for (let token = children.head; token; token = token.next) {
+					if (token.data.children) {
+						findURLToken(url, token.data.children, callback);
+					}
+					if (token.data.type == "Url" && DOM.removeQuotes(DomUtil.getCSSValue(token.data.value)) == url) {
+						callback(token, children);
+					}
+				}
+			}
 		}
 
 		static async processAttribute(doc, resourceElements, attributeName, prefixDataURI, baseURI, options, cssVariables, styles, batchRequest, processDuplicates, removeElementIfMissing) {