src/vs/workbench/contrib/webviewPanel/browser/webviewIconManager.ts/WebviewIconManager/styleElement
class WebviewIconManager:	private get styleElement(): HTMLStyleElement {
		if (!this._styleElement) {
			this._styleElement = dom.createStyleSheet();
			this._styleElement.className = 'webview-icons';
		}
		return this._styleElement;
	}