More updates for Athena v1.1.1+ compatibility

[cjg89]

Description

• Removed $small-font-size override in the theme to allow this variable to inherit adjustments from Athena v1.1.1.
• Added underline styles on hover, focus to .list-chevrons links.

This PR should hopefully wrap up the last remaining theme style adjustments necessary to support Athena v1.1.1.

Motivation and Context

Resolves #129.

How Has This Been Tested?

Tested in Dev.

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [x] My code follows the code style of this project.
• [ ] My change requires an update to the documentation.
• [ ] I have updated the documentation accordingly.