Manually add no-descending-specificity and refactor to pass linting

[benjamincharity]

We held off integrating this rule as it would require a good bit of style refactoring. We should still attempt this refactor in an isolated branch as it's good practice to not have descending specificity.

https://stylelint.io/user-guide/rules/no-descending-specificity/

---

• Integrate the rule into our repo
• Refactor styles as needed
• Visually verify all components have not changed
• Open an issue in https://github.com/GetTerminus/stylelint-config-frontend/issues to support that rule in our shared config