Unify styles libraries for Desktop
### Description
Create a single library for Desktop styles. This will be done by exporting Mozilla's Figma files as .fig then importing them into our organization. The next step will be to adjust the styles according to Tor Browser's context and publish the libraries so they can be used in the following steps.
**Note:** the styles may need adjustments through the whole process while being applied to components and screens.
### Scope
- Desktop colors
- Desktop shadows
- Desktop typography (for both Windows and Mac)
### Design estimate
- Complexity: medium (3 days)
- Uncertainty: moderate (1.5)
- Total: 4-4.5 days
- Actual: 3 days
### Checklist
- [x] Export Mozilla's files
- [x] Import files to Tor Project UX
- [x] Clean unnecessary elements
- [x] Adjust variables/styles according to TB
- [x] Adjust documentation for TB's context
- [x] Publish library
### Figma file
[Link to the file](https://www.figma.com/design/ZaHzSYjtItR3VVcSrtARl9/Desktop-Styles?node-id=14-523&t=J9UlSuQwuynxhiY9-1)
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