## Problem
In Kanban view, clicking the `Empty` value for the Member property can
cause the member popover layout to overflow/break due to a fixed
container width.
### Before ScreenShot
<img width="410" height="119" alt="image"
src="https://github.com/user-attachments/assets/e0d28a37-2ea4-4a65-afca-e4ef10af37dd"
/>
## Repro
1. Open a Database in Kanban view
2. Ensure the Member property has some cards with `Empty`
3. Click the `Empty` member value
4. Observe the popover layout overflow/broken UI
## Solution
Make the popover container responsive by using `width: 100%` with
`maxWidth: 415px` to preserve the original intended size while
preventing overflow in narrow containers.
### After ScreenShot
<img width="410" height="146" alt="image (1)"
src="https://github.com/user-attachments/assets/d97e6b8b-eabc-499a-9f04-0422505c67bf"
/>
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit
* **Style**
* Improved member selector popover styling: unified padding, made width
responsive with a max width limit, and added box-sizing for more
consistent layout and spacing across screen sizes.
<sub>✏️ Tip: You can customize this high-level summary in your review
settings.</sub>
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
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