The "Shot expired" and "Leave Screenshots" pages should also have a white background

[SoftVision-CosminMuntean]

[Affected versions]:

• Nightly 64.0a1
• Screenshots 34.0.0 dev

[Affected Platforms]:

• All Windows
• All Mac
• All Linux

[Prerequisites]:

• The "xpinstall.signatures.required" boolean pref is set to "false".
• The "extensions.legacy.enabled" boolean pref is set tot "true".
• Have the Screenshots 34.0.0 dev version installed from here, on a new clean profile.

[Steps to reproduce]:

1. Open the Firefox browser with the profile from prerequisites.
2. Navigate to any website and save a selection.
3. Click the "Remove All Data" link from the footer of the page.
4. Observe the background of the "Leave Screenshots" page.
5. Observe the "Page not found" page.

[Expected result]:

• The background of the page is white.

[Actual results]:

• The background of the page is dark gray.

[Notes]:

• Here is a screenshot of a "Shot expired" page:
  

• Here is a screenshot of a "Leave Screenshots" page:
  

[punamdahiya]

Fixed with #5065

[SoftVision-CosminMuntean]

I have verified this issue and the "Shot expired" and "Leave Screenshots" pages have a white background on latest Screenshtos dev version.