View Transitions admin opt-in checkbox appears stretched on mobile

## Bug Description



I loaded the Reading screen on mobile to enable View Transitions in the admin, but the checkbox styling is unexpected in how it is stretched wide:

<img width="1008" height="639" alt="Image" src="https://github.com/user-attachments/assets/c1609a2f-a568-4752-9437-aad70797e8e1" />