src/vs/workbench/contrib/webviewPanel/browser/webviewIconManager.ts/WebviewIconManager/updateStyleSheet
class WebviewIconManager:	private async updateStyleSheet() {
		await this._lifecycleService.when(LifecyclePhase.Starting);

		const cssRules: string[] = [];
		if (this._configService.getValue('workbench.iconTheme') !== null) {
			for (const [key, value] of this._icons) {
				const webviewSelector = `.show-file-icons .webview-${key}-name-file-icon::before`;
				try {
					cssRules.push(
						`.monaco-workbench.vs ${webviewSelector} { content: ""; background-image: ${dom.asCSSUrl(value.light)}; }`,
						`.monaco-workbench.vs-dark ${webviewSelector}, .monaco-workbench.hc-black ${webviewSelector} { content: ""; background-image: ${dom.asCSSUrl(value.dark)}; }`
					);
				} catch {
					// noop
				}
			}
		}
		this.styleElement.textContent = cssRules.join('\n');
	}