src/vs/base/browser/ui/splitview/paneview.ts/PaneView/focusPrevious
class PaneView:	private focusPrevious(): void {
		const headers = this.getPaneHeaderElements();
		const index = headers.indexOf(document.activeElement as HTMLElement);

		if (index === -1) {
			return;
		}

		headers[Math.max(index - 1, 0)].focus();
	}