The Preview Collections tab overlays the entire screen with a white background

[Onokaev]

Describe the bug
After adding resources to a collection and clicking on 'Preview Collection', the overlay applied is white by default. It should blend in with the set theme

To Reproduce
Steps to reproduce the behavior:

1. Go to https://developer.microsoft.com/en-us/graph/graph-explorer
2. Click on Resources
3. Click on any kebab menu
4. Click on 'Add to collections'
5. Click on Preview collections
6. Notice that the area outside the panel is completely white

Expected behavior
The overlay should be consistent with other panel overlays e.g Permissions panel overlay

Screenshots

Desktop (please complete the following information):

• OS: [e.g. iOS]
• Browser [e.g. chrome, safari]
• Version [e.g. 22]

Smartphone (please complete the following information):

• Device: [e.g. iPhone6]
• OS: [e.g. iOS8.1]
• Browser [e.g. stock browser, safari]
• Version [e.g. 22]

Additional context
Add any other context about the problem here.