Fixed broken layout issue with collapse field

[girishpanchal30]

Summary

I've fixed the broken layout and fixed PHP warning in the functions.php file.

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• I have written a test and included it in this PR
• I have run all tests and they pass
• The code passes when running the PHP CodeSniffer
• Code meets WordPress Coding Standards for PHP, HTML, CSS and JS
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Closes https://github.com/Codeinwp/ppom-pro/issues/454

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