Fix / ensure modals overlap underlying elements

[MelissaDTH]

Description

• This PR enhances the modal overlay functionality by explicitly setting z-index: 0 on the .layout class, ensuring a consistent stacking order. Previously, the z-index defaulted to auto, certain elements beneath an opened modal (e.g., the sign up modal or Player) remained visible. This adjustment establishes a clear stacking context, effectively positioning .layout below other elements and resolving the issue of elements showing through the modal overlay.

Example of initial bug

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