The toggle works, but the implementation is hard to live with in a real app:

• State lives in window globals instead of a Client Variable, so GetCurrentMode is wrong until the block has rendered.
• The block CSS forces !important rules on body, inputs and any class containing "card"/"panel", overriding the app theme and OutSystems UI.
• Colour palettes are hard-coded in JavaScript and duplicated across three actions; the theme should own colours, the component should only switch a data-theme attribute.
• Runs in OnReady, so every page load flashes light before going dark; a global transition style is injected and never removed.
• No accessibility (Link with no label, no role="switch"), console.log everywhere, errors silently swallowed, mandatory event, no descriptions.