update style.textContent instead of calling insertRule, #75061

this change makes style changes visible to the mutation observer

src/vs/base/browser/dom.ts

@@ -804,8 +804,7 @@ export function createCSSRule(selector: string, cssText: string, style: HTMLStyl
 	if (!style || !cssText) {
 		return;
 	}
-
-	(<CSSStyleSheet>style.sheet).insertRule(selector + '{' + cssText + '}', 0);
+	style.textContent = `${selector}{${cssText}}\n${style.textContent}`;
 }
 
 export function removeCSSRulesContainingSelector(ruleName: string, style: HTMLStyleElement = getSharedStyleSheet()): void {