Fixed challenge listing container not taking full height

[Pratik1005]

Challenge listing container not taking full height #498

Title : Challenge listing container not taking full height

Issue No. : #498

Code Stack : Native (HTML, CSS, and JS)

Close #498

Checklist:

• [] I have mentioned the issue number in my Pull Request.
• [] I have commented my code, particularly in hard-to-understand areas
• [] I have created a helpful and easy to understand README.md
• [] I have updated the Index.html file for my contribution

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[sadanandpai]

Issue with 100vh @Pratik1005