Update chart/metrics sizing for template 3.0

[aloftus23]

fixes #269

🗣 Description

Adjusts report_generator.py, metrics.py, pages.py, and style.css to fit latest template 3.0.

💭 Motivation and context

Styling no longer fits the new template.

🧪 Testing

Passes pre-commits and pytests.

✅ Pre-approval checklist

• This PR has an informative and human-readable title.
• Changes are limited to a single goal - eschew scope creep!
• All future TODOs are captured in issues, which are referenced
  in code comments.
• All relevant type-of-change labels have been added.
• I have read the CONTRIBUTING document.
• These code changes follow cisagov code standards.
• All relevant repo and/or project documentation has been updated
  to reflect the changes in this PR.
• Tests have been added and/or modified to cover the changes in this PR.
• All new and existing tests pass.