feature(alert theming): Add theming to alert

[whymarlene]

Description

Closes #130

Adds theming to alert component

Type of change

🆕 Feature

How to Test

Visually and yarn test

Checklist

• [ ] Code follows design and style guidelines
• [ ] Code is commented with doc blocks
• [ ] Latest code has been rebased from base branch (usually develop)
• [ ] Commits follow guidelines (concise, squashed, etc)
• [ ] Github issues have been linked in relevant commits
• [ ] Relevant reviewers (EM) have been assigned to this PR

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