src/vs/editor/contrib/zoneWidget/browser/zoneWidget.ts/ZoneWidget/setCssClass
class ZoneWidget:	protected setCssClass(className: string, classToReplace?: string): void {
		if (!this.container) {
			return;
		}

		if (classToReplace) {
			this.container.classList.remove(classToReplace);
		}

		this.container.classList.add(className);

	}