src/vs/workbench/browser/parts/views/viewPaneContainer.ts/ViewPaneDropOverlay/doUpdateOverlayBorder
class ViewPaneDropOverlay:	private doUpdateOverlayBorder(direction: DropDirection | undefined): void {
		this.overlay.style.borderTopWidth = direction === DropDirection.UP ? '2px' : '0px';
		this.overlay.style.borderLeftWidth = direction === DropDirection.LEFT ? '2px' : '0px';
		this.overlay.style.borderBottomWidth = direction === DropDirection.DOWN ? '2px' : '0px';
		this.overlay.style.borderRightWidth = direction === DropDirection.RIGHT ? '2px' : '0px';
	}