fix: correct visual oddities and make styles more mobile-friendly

[asherlloyd]

Description

Resolves various visual oddities related to the app container, specifically on smaller resolutions.

Reason

Incorrect CSS style rules were resulting in a poor user experience caused by elements not fully expanding to fill parent heights.

How this has been tested

Locally, via the frontend build.

Types of changes

• [ ] New feature (adds functionality)
• [x] Bug fix (fixes an issue)
• [ ] Breaking changes (causes defects to existing pieces)

Screenshots

Before:

After:

Checklist:

• [x] I have read and complied with the CONTRIBUTING document
• [ ] The changes I've made follow the existing code style and formatting requirements
• [ ] My changes require updates to the documentation, which I have modified accordingly