feat: Dark Mode

[lanesawyer]

Dark Mode

Structural Element (Base, Gene, DNA, Chromosome or Cell) Github issue: #XXXX Copy isuue descirption here

Remaining Work

• [ ] Real dark mode colors
• [ ] Checking all the components to make sure nothing is broken
• [ ] Accessibility verification
• [ ] Updated documentation for setting up the project since you'll need to provide a theme now (or, we just default to light or something)
• [ ] Probably other things I'm forgetting

Checklist

• [ ] Default Story in Storybook
• [ ] LivePreview Story in Storybook
• [ ] Test Story in Storybook
• [ ] Tests written
• [ ] Variables from defaultTheme.ts used wherever possible
• [ ] If updating an existing component, depreciate flag has been used where necessary
• [ ] Chromatic build verified by @chanzuckerberg/sds-design