Create Teams Dark Theme Variables

[levithomason]

We need to create dark theme variables for all components. We will first do this explicitly in siteVariables and each component's variables file. Afterward, we can consider an abstraction for applying "color schemes" to components. Let's wait on that until we can see the pattern that emerges.

Please link you PR after the item you are completing below.

Doc Site

• ComponentExample.tsx background should change on theme switch feat: give component examples a theme specific background #316
• (Low priority) theme switcher for each Component Example

Components P1

• Button @bcalvery BREAKING: Button - implement dark theme and match redlines #336
• Button Contrast @bcalvery fix(Button): Implementing Contrast Theme and Updating Dark Theme #381
• Divider @codepretty feat(Divider): Redlining divider component for Teams dark & contrast themes #338
• Header @bcalvery
• Icon
• Image
• Layout
• Segment
• Text @codepretty feat(Text): Redlining text component for Teams dark & contrast themes #317

Components P2

• Accordion
• Attachment
• Avatar @bcalvery fix(Avatar): Adding dark and contrast theme files for Avatar and Status Indicator. #373
• Chat
• Grid
• Input
• ItemLayout
• Label
• List
• Menu
• Popup
• Portal
• RadioGroup
• Status @bcalvery fix(Avatar): Adding dark and contrast theme files for Avatar and Status Indicator. #373

[levithomason]

/cc @codepretty, @notandrew, @sergiorv, @bcalvery, @alinais, @mnajdova

[codepretty]

We are doing Dark theme & Contrast theme at the same time, so it is unnecessary to keep 2 separate issues for this. Merged this issue into #349