You can just add an action after the “Show, treat as lightbox” to bring other widgets to front. Or, you can add a Shown event for your foreground widget with this Bring To Front action.
My first thought was that you’d need to group all your widgets together or place them together in a dynamic panel, to have one widget to “show” with the lightbox background behind them. This does work, but you need an extra Show action for your target “foreground element” and then a way to hide just that element and not the group. This also has an odd side effect of leaving that foreground element shown if the lightbox background is clicked–which dismisses the lightbox and hides the shown widget. …Only in this case, the widget to be shown (the group) is already shown, so it doesn’t work quite right.
Here is a quick demo, with standard behavior on Page 1, the grouping attempt on Page 2, and the solution on Page 3.
lightbox behavior.rp (78.2 KB)