Scan: Fix all bugs on mobile screen

[pzshine]

Implementation details

• Added background when the mobile menu is opened.
• Removed the extra space on the mobile screen.
• Fixed N/A state on validator homepage
• Improved the layout on validator index (top part)

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• The pull request includes any and all appropriate unit/integration tests
• You have added a relevant changelog entry to CHANGELOG_UNRELEASED.md
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