diff --git a/packages/happy-dom/src/css/declaration/AbstractCSSStyleDeclaration.ts b/packages/happy-dom/src/css/declaration/AbstractCSSStyleDeclaration.ts
index 739a381e9..19895a36e 100644
--- a/packages/happy-dom/src/css/declaration/AbstractCSSStyleDeclaration.ts
+++ b/packages/happy-dom/src/css/declaration/AbstractCSSStyleDeclaration.ts
@@ -86,6 +86,10 @@ export default abstract class AbstractCSSStyleDeclaration {
 					this._ownerElement['_attributes']['style'].name = 'style';
 				}
 
+				if (this._ownerElement.isConnected) {
+					this._ownerElement.ownerDocument['_cacheID']++;
+				}
+
 				this._ownerElement['_attributes']['style'].value = style.toString();
 			}
 		} else {
@@ -137,6 +141,10 @@ export default abstract class AbstractCSSStyleDeclaration {
 			const style = this._elementStyle.getElementStyle();
 			style.set(name, value, !!priority);
 
+			if (this._ownerElement.isConnected) {
+				this._ownerElement.ownerDocument['_cacheID']++;
+			}
+
 			this._ownerElement['_attributes']['style'].value = style.toString();
 		} else {
 			this._style.set(name, value, !!priority);
@@ -163,6 +171,10 @@ export default abstract class AbstractCSSStyleDeclaration {
 			style.remove(name);
 			const newCSSText = style.toString();
 			if (newCSSText) {
+				if (this._ownerElement.isConnected) {
+					this._ownerElement.ownerDocument['_cacheID']++;
+				}
+
 				this._ownerElement['_attributes']['style'].value = newCSSText;
 			} else {
 				delete this._ownerElement['_attributes']['style'];
diff --git a/packages/happy-dom/src/css/declaration/utilities/CSSStyleDeclarationElementStyle.ts b/packages/happy-dom/src/css/declaration/utilities/CSSStyleDeclarationElementStyle.ts
index 686ed4659..de3749d17 100644
--- a/packages/happy-dom/src/css/declaration/utilities/CSSStyleDeclarationElementStyle.ts
+++ b/packages/happy-dom/src/css/declaration/utilities/CSSStyleDeclarationElementStyle.ts
@@ -12,14 +12,29 @@ import CSSStyleRule from '../../rules/CSSStyleRule';
 import CSSStyleDeclarationElementDefaultCSS from './CSSStyleDeclarationElementDefaultCSS';
 import CSSStyleDeclarationElementInheritedProperties from './CSSStyleDeclarationElementInheritedProperties';
 import CSSStyleDeclarationCSSParser from './CSSStyleDeclarationCSSParser';
+import QuerySelector from '../../../query-selector/QuerySelector';
 
 const CSS_VARIABLE_REGEXP = /var\( *(--[^) ]+)\)/g;
 
+type IStyleAndElement = {
+	element: IElement | IShadowRoot | IDocument;
+	cssTexts: Array<{ cssText: string; priorityWeight: number }>;
+};
+
 /**
  * CSS Style Declaration utility
  */
 export default class CSSStyleDeclarationElementStyle {
-	private cache: { [k: string]: CSSStyleDeclarationPropertyManager } = {};
+	private cache: {
+		propertyManager: CSSStyleDeclarationPropertyManager;
+		cssText: string;
+		documentCacheID: number;
+	} = {
+		propertyManager: null,
+		cssText: null,
+		documentCacheID: null
+	};
+
 	private element: IElement;
 	private computed: boolean;
 
@@ -47,11 +62,12 @@ export default class CSSStyleDeclarationElementStyle {
 		const cssText = this.element['_attributes']['style']?.value;
 
 		if (cssText) {
-			if (this.cache[cssText]) {
-				return this.cache[cssText];
+			if (this.cache.propertyManager && this.cache.cssText === cssText) {
+				return this.cache.propertyManager;
 			}
-			this.cache[cssText] = new CSSStyleDeclarationPropertyManager({ cssText });
-			return this.cache[cssText];
+			this.cache.cssText = cssText;
+			this.cache.propertyManager = new CSSStyleDeclarationPropertyManager({ cssText });
+			return this.cache.propertyManager;
 		}
 
 		return new CSSStyleDeclarationPropertyManager();
@@ -64,28 +80,37 @@ export default class CSSStyleDeclarationElementStyle {
 	 * @returns Style sheets.
 	 */
 	private getComputedElementStyle(): CSSStyleDeclarationPropertyManager {
-		const documentElements: Array<{ element: IElement; cssText: string }> = [];
-		const parentElements: Array<{ element: IElement; cssText: string }> = [];
-		let styleAndElement = {
+		const documentElements: Array<IStyleAndElement> = [];
+		const parentElements: Array<IStyleAndElement> = [];
+		let styleAndElement: IStyleAndElement = {
 			element: <IElement | IShadowRoot | IDocument>this.element,
-			cssText: ''
+			cssTexts: []
 		};
-		let shadowRootElements: Array<{ element: IElement; cssText: string }> = [];
+		let shadowRootElements: Array<IStyleAndElement> = [];
 
 		if (!this.element.isConnected) {
 			return new CSSStyleDeclarationPropertyManager();
 		}
 
+		if (
+			this.cache.propertyManager &&
+			this.cache.documentCacheID === this.element.ownerDocument['_cacheID']
+		) {
+			return this.cache.propertyManager;
+		}
+
+		this.cache.documentCacheID = this.element.ownerDocument['_cacheID'];
+
 		// Walks through all parent elements and stores them in an array with element and matching CSS text.
 		while (styleAndElement.element) {
 			if (styleAndElement.element.nodeType === NodeTypeEnum.elementNode) {
 				const rootNode = styleAndElement.element.getRootNode();
 				if (rootNode.nodeType === NodeTypeEnum.documentNode) {
-					documentElements.unshift(<{ element: IElement; cssText: string }>styleAndElement);
+					documentElements.unshift(styleAndElement);
 				} else {
-					shadowRootElements.unshift(<{ element: IElement; cssText: string }>styleAndElement);
+					shadowRootElements.unshift(styleAndElement);
 				}
-				parentElements.unshift(<{ element: IElement; cssText: string }>styleAndElement);
+				parentElements.unshift(styleAndElement);
 			}
 
 			if (styleAndElement.element === this.element.ownerDocument) {
@@ -103,7 +128,7 @@ export default class CSSStyleDeclarationElementStyle {
 					}
 				}
 
-				styleAndElement = { element: null, cssText: '' };
+				styleAndElement = { element: null, cssTexts: [] };
 			} else if ((<IShadowRoot>styleAndElement.element).host) {
 				const styleSheets = <INodeList<IHTMLStyleElement>>(
 					(<IShadowRoot>styleAndElement.element).querySelectorAll('style,link[rel="stylesheet"]')
@@ -111,7 +136,7 @@ export default class CSSStyleDeclarationElementStyle {
 
 				styleAndElement = {
 					element: <IElement>(<IShadowRoot>styleAndElement.element).host,
-					cssText: ''
+					cssTexts: []
 				};
 
 				for (const styleSheet of styleSheets) {
@@ -120,39 +145,58 @@ export default class CSSStyleDeclarationElementStyle {
 						this.parseCSSRules({
 							elements: shadowRootElements,
 							cssRules: sheet.cssRules,
-							hostElement: <{ element: IElement; cssText: string }>styleAndElement
+							hostElement: styleAndElement
 						});
 					}
 				}
 				shadowRootElements = [];
 			} else {
-				styleAndElement = { element: <IElement>styleAndElement.element.parentNode, cssText: '' };
+				styleAndElement = { element: <IElement>styleAndElement.element.parentNode, cssTexts: [] };
 			}
 		}
 
 		// Concatenates all parent element CSS to one string.
 		const targetElement = parentElements[parentElements.length - 1];
-		let inheritedCSSText = CSSStyleDeclarationElementDefaultCSS.default;
+		let inheritedCSSText = '';
 
 		for (const parentElement of parentElements) {
 			if (parentElement !== targetElement) {
-				inheritedCSSText +=
-					(CSSStyleDeclarationElementDefaultCSS[parentElement.element.tagName] || '') +
-					parentElement.cssText +
-					(parentElement.element['_attributes']['style']?.value || '');
+				parentElement.cssTexts.sort((a, b) => a.priorityWeight - b.priorityWeight);
+
+				if (CSSStyleDeclarationElementDefaultCSS[(<IElement>parentElement.element).tagName]) {
+					inheritedCSSText +=
+						CSSStyleDeclarationElementDefaultCSS[(<IElement>parentElement.element).tagName];
+				}
+
+				for (const cssText of parentElement.cssTexts) {
+					inheritedCSSText += cssText.cssText;
+				}
+
+				if (parentElement.element['_attributes']['style']?.value) {
+					inheritedCSSText += parentElement.element['_attributes']['style'].value;
+				}
 			}
 		}
 
 		const cssVariables: { [k: string]: string } = {};
 		const properties = {};
-		const targetCSSText =
-			(CSSStyleDeclarationElementDefaultCSS[targetElement.element.tagName] || '') +
-			targetElement.cssText +
-			(targetElement.element['_attributes']['style']?.value || '');
+		let targetCSSText =
+			CSSStyleDeclarationElementDefaultCSS[(<IElement>targetElement.element).tagName] || '';
+
+		targetElement.cssTexts.sort((a, b) => a.priorityWeight - b.priorityWeight);
+
+		for (const cssText of targetElement.cssTexts) {
+			targetCSSText += cssText.cssText;
+		}
+
+		if (targetElement.element['_attributes']['style']?.value) {
+			targetCSSText += targetElement.element['_attributes']['style'].value;
+		}
+
 		const combinedCSSText = inheritedCSSText + targetCSSText;
 
-		if (this.cache[combinedCSSText]) {
-			return this.cache[combinedCSSText];
+		if (this.cache.propertyManager && this.cache.cssText === combinedCSSText) {
+			return this.cache.propertyManager;
 		}
 
 		// Parses the parent element CSS and stores CSS variables and inherited properties.
@@ -204,7 +248,8 @@ export default class CSSStyleDeclarationElementStyle {
 			propertyManager.set(name, properties[name].value, properties[name].important);
 		}
 
-		this.cache[combinedCSSText] = propertyManager;
+		this.cache.cssText = combinedCSSText;
+		this.cache.propertyManager = propertyManager;
 
 		return propertyManager;
 	}
@@ -216,13 +261,11 @@ export default class CSSStyleDeclarationElementStyle {
 	 * @param options.elements Elements.
 	 * @param options.cssRules CSS rules.
 	 * @param [options.hostElement] Host element.
-	 * @param [options.hostElement.element] Element.
-	 * @param [options.hostElement.cssText] CSS text.
 	 */
 	private parseCSSRules(options: {
 		cssRules: CSSRule[];
-		elements: Array<{ element: IElement; cssText: string }>;
-		hostElement?: { element: IElement; cssText: string };
+		elements: Array<IStyleAndElement>;
+		hostElement?: IStyleAndElement;
 	}): void {
 		if (!options.elements.length) {
 			return;
@@ -236,12 +279,19 @@ export default class CSSStyleDeclarationElementStyle {
 				if (selectorText) {
 					if (selectorText.startsWith(':host')) {
 						if (options.hostElement) {
-							options.hostElement.cssText += (<CSSStyleRule>rule)._cssText;
+							options.hostElement.cssTexts.push({
+								cssText: (<CSSStyleRule>rule)._cssText,
+								priorityWeight: 0
+							});
 						}
 					} else {
 						for (const element of options.elements) {
-							if (element.element.matches(selectorText)) {
-								element.cssText += (<CSSStyleRule>rule)._cssText;
+							const matchResult = QuerySelector.match(element.element, selectorText);
+							if (matchResult.matches) {
+								element.cssTexts.push({
+									cssText: (<CSSStyleRule>rule)._cssText,
+									priorityWeight: matchResult.priorityWeight
+								});
 							}
 						}
 					}
diff --git a/packages/happy-dom/src/nodes/character-data/CharacterData.ts b/packages/happy-dom/src/nodes/character-data/CharacterData.ts
index 0a3875e90..5d039ca94 100644
--- a/packages/happy-dom/src/nodes/character-data/CharacterData.ts
+++ b/packages/happy-dom/src/nodes/character-data/CharacterData.ts
@@ -56,6 +56,10 @@ export default abstract class CharacterData extends Node implements ICharacterDa
 		const oldValue = this._data;
 		this._data = data;
 
+		if (this.isConnected) {
+			this.ownerDocument['_cacheID']++;
+		}
+
 		// MutationObserver
 		if (this._observers.length > 0) {
 			for (const observer of this._observers) {
diff --git a/packages/happy-dom/src/nodes/document/Document.ts b/packages/happy-dom/src/nodes/document/Document.ts
index bcf51a28b..1e1493a2d 100644
--- a/packages/happy-dom/src/nodes/document/Document.ts
+++ b/packages/happy-dom/src/nodes/document/Document.ts
@@ -60,6 +60,10 @@ export default class Document extends Node implements IDocument {
 	public readonly defaultView: IWindow;
 	public readonly _readyStateManager: DocumentReadyStateManager;
 	public _activeElement: IHTMLElement = null;
+
+	// Used as an unique identifier which is updated whenever the DOM gets modified.
+	public _cacheID = 0;
+
 	protected _isFirstWrite = true;
 	protected _isFirstWriteAfterOpen = false;
 	private _cookie = '';
diff --git a/packages/happy-dom/src/nodes/element/Element.ts b/packages/happy-dom/src/nodes/element/Element.ts
index 0cf926b6f..a90f3a487 100644
--- a/packages/happy-dom/src/nodes/element/Element.ts
+++ b/packages/happy-dom/src/nodes/element/Element.ts
@@ -5,7 +5,6 @@ import DOMRect from './DOMRect';
 import DOMTokenList from '../../dom-token-list/DOMTokenList';
 import IDOMTokenList from '../../dom-token-list/IDOMTokenList';
 import QuerySelector from '../../query-selector/QuerySelector';
-import SelectorItem from '../../query-selector/SelectorItem';
 import MutationRecord from '../../mutation-observer/MutationRecord';
 import MutationTypeEnum from '../../mutation-observer/MutationTypeEnum';
 import NamespaceURI from '../../config/NamespaceURI';
@@ -744,12 +743,7 @@ export default class Element extends Node implements IElement {
 	 * @returns "true" if matching.
 	 */
 	public matches(selector: string): boolean {
-		for (const part of selector.split(',')) {
-			if (new SelectorItem(part.trim()).match(this)) {
-				return true;
-			}
-		}
-		return false;
+		return QuerySelector.match(this, selector).matches;
 	}
 
 	/**
@@ -852,6 +846,10 @@ export default class Element extends Node implements IElement {
 		(<IElement>attribute.ownerElement) = <IElement>this;
 		(<IDocument>attribute.ownerDocument) = this.ownerDocument;
 
+		if (this.isConnected) {
+			this.ownerDocument['_cacheID']++;
+		}
+
 		this._attributes[name] = attribute;
 
 		this._updateDomListIndices();
@@ -937,6 +935,10 @@ export default class Element extends Node implements IElement {
 	public removeAttributeNode(attribute: IAttr): void {
 		delete this._attributes[attribute.name];
 
+		if (this.isConnected) {
+			this.ownerDocument['_cacheID']++;
+		}
+
 		this._updateDomListIndices();
 
 		if (
diff --git a/packages/happy-dom/src/nodes/node/Node.ts b/packages/happy-dom/src/nodes/node/Node.ts
index 35799a2d0..ae2cc05a5 100644
--- a/packages/happy-dom/src/nodes/node/Node.ts
+++ b/packages/happy-dom/src/nodes/node/Node.ts
@@ -308,6 +308,10 @@ export default class Node extends EventTarget implements INode {
 			}
 		}
 
+		if (this.isConnected) {
+			(this.ownerDocument || this)['_cacheID']++;
+		}
+
 		this.childNodes.push(node);
 
 		(<Node>node)._connectToNode(this);
@@ -345,6 +349,10 @@ export default class Node extends EventTarget implements INode {
 			throw new DOMException('Failed to remove node. Node is not child of parent.');
 		}
 
+		if (this.isConnected) {
+			(this.ownerDocument || this)['_cacheID']++;
+		}
+
 		this.childNodes.splice(index, 1);
 
 		(<Node>node)._connectToNode(null);
@@ -404,6 +412,10 @@ export default class Node extends EventTarget implements INode {
 			);
 		}
 
+		if (this.isConnected) {
+			(this.ownerDocument || this)['_cacheID']++;
+		}
+
 		if (newNode.parentNode) {
 			const index = newNode.parentNode.childNodes.indexOf(newNode);
 			if (index !== -1) {
diff --git a/packages/happy-dom/src/query-selector/QuerySelector.ts b/packages/happy-dom/src/query-selector/QuerySelector.ts
index ceab058e7..31bf010bc 100644
--- a/packages/happy-dom/src/query-selector/QuerySelector.ts
+++ b/packages/happy-dom/src/query-selector/QuerySelector.ts
@@ -8,9 +8,6 @@ import NodeListFactory from '../nodes/node/NodeListFactory';
 
 const SELECTOR_PART_REGEXP = /(\[[^\]]+\]|[a-zA-Z0-9-_.#"*:()\]]+)|([ ,>]+)/g;
 
-// The above one seem to work fine and is faster, but this one can be useful if more rules need to be added as it is more "correct".
-// Const SELECTOR_PART_REGEXP = /([a-zA-Z0-9-$.]+|\[[a-zA-Z0-9-]+\]|\[[a-zA-Z0-9$-~|^$*]+[ ]*=[ ]*"[^"]+"\])|([ ,]+)/g;
-
 /**
  * Utility for query selection in an HTML element.
  *
@@ -57,6 +54,70 @@ export default class QuerySelector {
 		return null;
 	}
 
+	/**
+	 * Checks if a node matches a selector and returns priority weight.
+	 *
+	 * @param node Node to search in.
+	 * @param selector Selector.
+	 * @returns Result.
+	 */
+	public static match(node: INode, selector: string): { priorityWeight: number; matches: boolean } {
+		for (const parts of this.getSelectorParts(selector)) {
+			const result = this.matchesSelector(node, node, parts.reverse());
+
+			if (result.matches) {
+				return result;
+			}
+		}
+
+		return { priorityWeight: 0, matches: false };
+	}
+
+	/**
+	 * Checks if a node matches a selector.
+	 *
+	 * @param targetNode Target node.
+	 * @param currentNode Current node.
+	 * @param selectorParts Selector parts.
+	 * @param [priorityWeight] Priority weight.
+	 * @returns Result.
+	 */
+	private static matchesSelector(
+		targetNode: INode,
+		currentNode: INode,
+		selectorParts: string[],
+		priorityWeight = 0
+	): {
+		priorityWeight: number;
+		matches: boolean;
+	} {
+		const isDirectChild = selectorParts[0] === '>';
+		if (isDirectChild) {
+			selectorParts = selectorParts.slice(1);
+			if (selectorParts.length === 0) {
+				return { priorityWeight: 0, matches: false };
+			}
+		}
+
+		if (selectorParts.length === 0) {
+			return { priorityWeight, matches: true };
+		}
+
+		const selector = new SelectorItem(selectorParts[0]);
+		const result = selector.match(<Element>currentNode);
+
+		if (targetNode === currentNode && !result.matches) {
+			return { priorityWeight: 0, matches: false };
+		}
+
+		return this.matchesSelector(
+			isDirectChild ? currentNode.parentNode : targetNode,
+			currentNode.parentNode,
+			selectorParts.slice(1),
+			priorityWeight + result.priorityWeight
+		);
+	}
+
 	/**
 	 * Finds elements based on a query selector for a part of a list of selectors separated with comma.
 	 *
@@ -81,7 +142,7 @@ export default class QuerySelector {
 
 		for (const node of nodes) {
 			if (node.nodeType === Node.ELEMENT_NODE) {
-				if (selector.match(<Element>node)) {
+				if (selector.match(<Element>node).matches) {
 					if (selectorParts.length === 1) {
 						if (rootNode !== node) {
 							matched.push(node);
@@ -125,7 +186,7 @@ export default class QuerySelector {
 		const selector = selectorItem || new SelectorItem(selectorParts[0]);
 
 		for (const node of nodes) {
-			if (node.nodeType === Node.ELEMENT_NODE && selector.match(<Element>node)) {
+			if (node.nodeType === Node.ELEMENT_NODE && selector.match(<Element>node).matches) {
 				if (selectorParts.length === 1) {
 					if (rootNode !== node) {
 						return <Element>node;
diff --git a/packages/happy-dom/src/query-selector/SelectorItem.ts b/packages/happy-dom/src/query-selector/SelectorItem.ts
index dc0b2389b..5c24fda9d 100644
--- a/packages/happy-dom/src/query-selector/SelectorItem.ts
+++ b/packages/happy-dom/src/query-selector/SelectorItem.ts
@@ -1,4 +1,5 @@
 import DOMException from '../exception/DOMException';
+import IElement from '../nodes/element/IElement';
 import Element from '../nodes/element/Element';
 
 const ATTRIBUTE_REGEXP =
@@ -13,12 +14,12 @@ const ID_REGEXP = /#[A-Za-z][-A-Za-z0-9_]*/g;
  * Selector item.
  */
 export default class SelectorItem {
-	public isAll: boolean;
-	public isID: boolean;
-	public isAttribute: boolean;
-	public isPseudo: boolean;
-	public isClass: boolean;
-	public isTagName: boolean;
+	private isAll: boolean;
+	private isID: boolean;
+	private isAttribute: boolean;
+	private isPseudo: boolean;
+	private isClass: boolean;
+	private isTagName: boolean;
 	private tagName = null;
 	private selector: string;
 	private id: string;
@@ -42,6 +43,7 @@ export default class SelectorItem {
 		this.isTagName = this.tagName !== null;
 		this.selector = selector;
 		this.id = null;
+
 		if (!this.isAll && this.isID) {
 			const idMatches = baseSelector.match(ID_REGEXP);
 			if (idMatches) {
@@ -54,46 +56,60 @@ export default class SelectorItem {
 	 * Matches a selector against an element.
 	 *
 	 * @param element HTML element.
-	 * @returns TRUE if matching.
+	 * @returns Result.
 	 */
-	public match(element: Element): boolean {
+	public match(element: IElement): { priorityWeight: number; matches: boolean } {
 		const selector = this.selector;
 
+		let priorityWeight = 0;
+
 		// Is all (*)
 		if (this.isAll) {
-			return true;
+			return { priorityWeight: 0, matches: true };
 		}
 
 		// ID Match
 		if (this.isID) {
+			priorityWeight += 100;
+
 			if (this.id !== element.id) {
-				return false;
+				return { priorityWeight: 0, matches: false };
 			}
 		}
 
 		// Tag name match
 		if (this.isTagName) {
+			priorityWeight += 1;
+
 			if (this.tagName !== element.tagName) {
-				return false;
+				return { priorityWeight: 0, matches: false };
 			}
 		}
 
 		// Class match
-		if (this.isClass && !this.matchesClass(element, selector)) {
-			return false;
+		if (this.isClass) {
+			const result = this.matchesClass(element, selector);
+			priorityWeight += result.priorityWeight;
+			if (!result.matches) {
+				return { priorityWeight: 0, matches: false };
+			}
 		}
 
 		// Pseudo match
 		if (this.isPseudo && !this.matchesPsuedo(element, selector)) {
-			return false;
+			return { priorityWeight: 0, matches: false };
 		}
 
 		// Attribute match
-		if (this.isAttribute && !this.matchesAttribute(element, selector)) {
-			return false;
+		if (this.isAttribute) {
+			const result = this.matchesAttribute(element, selector);
+			priorityWeight += result.priorityWeight;
+			if (!result.matches) {
+				return { priorityWeight: 0, matches: false };
+			}
 		}
 
-		return true;
+		return { priorityWeight, matches: true };
 	}
 
 	/**
@@ -103,7 +119,7 @@ export default class SelectorItem {
 	 * @param selector Selector.
 	 * @returns True if it is a match.
 	 */
-	private matchesPsuedo(element: Element, selector: string): boolean {
+	private matchesPsuedo(element: IElement, selector: string): boolean {
 		const regexp = new RegExp(PSUEDO_REGEXP, 'g');
 		let match: RegExpMatchArray;
 
@@ -113,8 +129,8 @@ export default class SelectorItem {
 				return false;
 			} else if (
 				match[3] &&
-				((isNotClass && this.matchesClass(element, match[3])) ||
-					(!isNotClass && this.matchesAttribute(element, match[3])))
+				((isNotClass && this.matchesClass(element, match[3]).matches) ||
+					(!isNotClass && this.matchesAttribute(element, match[3])).matches)
 			) {
 				return false;
 			} else if (match[4] && !this.matchesPsuedoExpression(element, match[4])) {
@@ -133,8 +149,8 @@ export default class SelectorItem {
 	 * @param place Place.
 	 * @returns True if it is a match.
 	 */
-	private matchesNthChild(element: Element, psuedo: string, place: string): boolean {
-		let children = element.parentNode ? (<Element>element.parentNode).children : [];
+	private matchesNthChild(element: IElement, psuedo: string, place: string): boolean {
+		let children = element.parentNode ? (<IElement>element.parentNode).children : [];
 
 		switch (psuedo.toLowerCase()) {
 			case 'nth-of-type':
@@ -188,8 +204,8 @@ export default class SelectorItem {
 	 * @param psuedo Psuedo name.
 	 * @returns True if it is a match.
 	 */
-	private matchesPsuedoExpression(element: Element, psuedo: string): boolean {
-		const parent = <Element>element.parentNode;
+	private matchesPsuedoExpression(element: IElement, psuedo: string): boolean {
+		const parent = <IElement>element.parentNode;
 
 		if (!parent) {
 			return false;
@@ -240,24 +256,31 @@ export default class SelectorItem {
 	 *
 	 * @param element Element.
 	 * @param selector Selector.
-	 * @returns True if it is a match.
+	 * @returns Result.
 	 */
-	private matchesAttribute(element: Element, selector: string): boolean {
+	private matchesAttribute(
+		element: IElement,
+		selector: string
+	): { priorityWeight: number; matches: boolean } {
 		const regexp = new RegExp(ATTRIBUTE_REGEXP, 'g');
 		let match: RegExpMatchArray;
+		let priorityWeight = 0;
 
 		while ((match = regexp.exec(selector))) {
 			const isPsuedo = match.index > 0 && selector[match.index - 1] === '(';
+
+			priorityWeight += 10;
+
 			if (
 				!isPsuedo &&
 				((match[1] && !this.matchesAttributeName(element, match[1])) ||
 					(match[2] && !this.matchesAttributeNameAndValue(element, match[2], match[4], match[3])))
 			) {
-				return false;
+				return { priorityWeight: 0, matches: false };
 			}
 		}
 
-		return true;
+		return { priorityWeight, matches: true };
 	}
 
 	/**
@@ -265,20 +288,26 @@ export default class SelectorItem {
 	 *
 	 * @param element Element.
 	 * @param selector Selector.
-	 * @returns True if it is a match.
+	 * @returns Result.
 	 */
-	private matchesClass(element: Element, selector: string): boolean {
+	private matchesClass(
+		element: IElement,
+		selector: string
+	): { priorityWeight: number; matches: boolean } {
 		const regexp = new RegExp(CLASS_REGEXP, 'g');
 		const classList = element.className.split(' ');
+		const classSelector = selector.split(':')[0];
+		let priorityWeight = 0;
 		let match: RegExpMatchArray;
 
-		while ((match = regexp.exec(selector.split(':')[0]))) {
+		while ((match = regexp.exec(classSelector))) {
+			priorityWeight += 10;
 			if (!classList.includes(match[1])) {
-				return false;
+				return { priorityWeight: 0, matches: false };
 			}
 		}
 
-		return true;
+		return { priorityWeight, matches: true };
 	}
 
 	/**
@@ -288,12 +317,12 @@ export default class SelectorItem {
 	 * @param attributeName Attribute name.
 	 * @returns True if it is a match.
 	 */
-	private matchesAttributeName(element: Element, attributeName: string): boolean {
+	private matchesAttributeName(element: IElement, attributeName: string): boolean {
 		if (ATTRIBUTE_NAME_REGEXP.test(attributeName)) {
 			throw new DOMException(`The selector "${this.selector}" is not valid.`);
 		}
 
-		return !!element._attributes[attributeName.toLowerCase()];
+		return !!(<Element>element)._attributes[attributeName.toLowerCase()];
 	}
 
 	/** .
@@ -314,12 +343,12 @@ export default class SelectorItem {
 	 * @param matchType
 	 */
 	private matchesAttributeNameAndValue(
-		element: Element,
+		element: IElement,
 		attributeName: string,
 		attributeValue: string,
 		matchType: string = null
 	): boolean {
-		const attribute = element._attributes[attributeName.toLowerCase()];
+		const attribute = (<Element>element)._attributes[attributeName.toLowerCase()];
 		const value = attributeValue;
 
 		if (ATTRIBUTE_NAME_REGEXP.test(attributeName)) {
diff --git a/packages/happy-dom/test/css/declaration/CSSStyleDeclaration.test.ts b/packages/happy-dom/test/css/declaration/CSSStyleDeclaration.test.ts
index 749b46402..5db6b0f43 100644
--- a/packages/happy-dom/test/css/declaration/CSSStyleDeclaration.test.ts
+++ b/packages/happy-dom/test/css/declaration/CSSStyleDeclaration.test.ts
@@ -2217,6 +2217,30 @@ describe('CSSStyleDeclaration', () => {
 			expect(declaration.getPropertyValue('text-transform')).toBe('uppercase');
 			expect(declaration.getPropertyPriority('text-transform')).toBe('important');
 		});
+
+		it('Is using a cache.', () => {
+			const declaration = new CSSStyleDeclaration(element);
+
+			document.body.appendChild(element);
+			element.setAttribute('style', `border: 2px solid green;border-radius: 2px;font-size: 12px;`);
+
+			declaration.getPropertyValue('border');
+			const elementStyle = declaration['_elementStyle'].getElementStyle();
+			declaration.getPropertyValue('border');
+			expect(elementStyle).toBe(declaration['_elementStyle'].getElementStyle());
+
+			const computedDeclaration = new CSSStyleDeclaration(element, true);
+
+			computedDeclaration.getPropertyValue('border');
+			const computedElementStyle = declaration['_elementStyle'].getElementStyle();
+			computedDeclaration.getPropertyValue('border');
+			expect(computedElementStyle).toBe(declaration['_elementStyle'].getElementStyle());
+
+			element.setAttribute('style', `border: 2px solid green;`);
+
+			expect(elementStyle).not.toBe(declaration['_elementStyle'].getElementStyle());
+			expect(computedElementStyle).not.toBe(declaration['_elementStyle'].getElementStyle());
+		});
 	});
 
 	describe('getPropertyPriority()', () => {
diff --git a/packages/happy-dom/test/window/Window.test.ts b/packages/happy-dom/test/window/Window.test.ts
index fceebab10..8c8a92837 100644
--- a/packages/happy-dom/test/window/Window.test.ts
+++ b/packages/happy-dom/test/window/Window.test.ts
@@ -249,8 +249,14 @@ describe('Window', () => {
 					cursor: pointer;
 				}
 
-				span {
+				div span {
 					border-radius: 1px !important;
+                    direction: ltr;
+				}
+
+				.mySpan {
+                    /* Should have higher priority because of the specifity of the rule */
+                    direction: rtl;
 				}
 
 				@media (min-width: 1024px) {
@@ -266,12 +272,14 @@ describe('Window', () => {
 				}
 			`;
 
+			element.className = 'mySpan';
 			elementStyle.innerHTML = `
 				span {
 					border: 1px solid #000;
 					border-radius: 2px; 
 					color: green;
 					cursor: default;
+                    direction: ltr;
 				}
 			`;
 
@@ -286,6 +294,7 @@ describe('Window', () => {
 			expect(computedStyle.borderRadius).toBe('1px');
 			expect(computedStyle.color).toBe('red');
 			expect(computedStyle.cursor).toBe('default');
+			expect(computedStyle.direction).toBe('rtl');
 		});
 
 		it('Returns a CSSStyleDeclaration object with computed styles from style sheets for elements in a HTMLShadowRoot.', () => {