[docs] Update flex parent demo to set min height for overlays

[cherniavskii]

Fixes #14881 (comment)

[mui-bot]

Deploy preview: https://deploy-preview-14900--material-ui-x.netlify.app/

Generated by 🚫 dangerJS against 05172a0

[michelengelen]

LGTM

[cherniavskii]

Rationale: #14901 (comment)

[k-rajat19]

@cherniavskii I didn't notice that you have created this PR 😅, I have just created #14901 to address that issue
Should I close it?

[sampain]

Would be great if the overlay had a minimum height instead. It's something you can do manually with some CSS.

Ex:

  '& .MuiDataGrid-overlayWrapper': {
    minHeight: '104px',
  },

Adding a minimum height on the flex container that you have to calculate based on the size of the overlay that you want seems a bit weird and it's a number that looks arbitrary. If I want a 104px overlay, I need to set a minHeight of 231px. 231px does't look great in the code and needs a comment above it to explain why it's such a specific number. It's also a number you have to change if you add a toolbar to the datagrid for example.

[cherniavskii]

Hey @sampain
I've opened #15202 to address this.

[cherniavskii]

Closing in favor of #15202