Clean up CSS for Phase 2

[jhung]

Is your feature request related to a problem?

In the push to have the first release, the app.css file is a bit messy.

Describe the solution you'd like

Clean-up should be done on the CSS file, and consider using a pre-processor if needed.

[jobara]

The approach taken in other sites, such as the IDRC site, is to use Sass and organize it based on the 7-1 pattern. We had also hoped to model the style after Cube CSS, but that might have gotten away from us, so it would be worth reviewing this as things are moved around.

[BlueSlug]

Once this work has been completed, the Contribution Guidelines (CONTRIBUTING.md) should be updated to reflect the new rules and conventions for styling.