[BUG] Data source selectable and readonly component are not consistent

[BionIT]

Describe the bug

• The height of the popover header should be consistent between the read-only and selectable
• The stroke around the header looks better in the read-only popover, the floating line between the search field and the header looks a bit weird. This might be a part of next item.
• It looks like additional padding is added to the selectable popover content

To Reproduce
Steps to reproduce the behavior:

1. Go to future playground
2. Go to security plugin or index management plugin
3. Go to main page vs details page
4. See problem

Expected behavior
A clear and concise description of what you expected to happen.

OpenSearch Version
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Dashboards Version
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Plugins

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Screenshots

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Host/Environment (please complete the following information):

• OS: [e.g. iOS]
• Browser and version [e.g. 22]

Additional context

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[zhyuanqi]

Will work on it.

[BionIT]

Awesome, thanks @zhyuanqi

[BionIT]

I believe this is fixed, please reopen if not @zhyuanqi