Hide custom fields for Trello

Trello always shows every custom field on the back of a card, and there is no way to turn that off. The REST API has a single display switch, display.cardFront, which only affects the card front and the list view, and a Power-Up cannot reach the card back either, because it runs in a sandboxed cross-origin iframe. That becomes a problem when a field is meant to be filled from a searchable list in a Power-Up badge. The field itself is plain text, so the card back offers a second way to edit the same value: by hand, with no list and no validation. Over time that surface fills the field with spelling variants of the same few values, which is exactly what the picker exists to prevent. This extension applies one stylesheet on trello.com that hides those rows, leaving the badge as the single place to edit the value. Nothing is migrated, moved or deleted - the field goes on storing the data exactly as before, and the value stays visible on the card front, in exports and in the mobile and desktop apps. It is a guardrail, not access control. - One CSS file, applied by the browser as a content script. There is no JavaScript at all. - No permissions, no host permissions, no background service worker, no network requests. The extension only ever sees trello.com; it cannot read your tabs, history or cookies. - Rows are matched by the field label and Trello's own data-testid attribute. If Trello changes that markup, the rules stop matching and the fields simply reappear - nothing breaks. Which rows are hidden is defined in the stylesheet, and is meant to be adapted to your own board.