Make default background color grey to make buttons/inputs/containers standout

[JElgar]

Description

This seems to align with the mocks and seems to look better across the board

Fixes #<issue_number> or taiga link

Checklist:

Creator

• The target branch is main
• I have updated the unreleased section of the change log
• I have reviewed the 'files changed' tab on github to ensure all changes are as expected
• I have added someone to review the pr

Reviewer

• I have verified the above are all completed
• I have run the code locally to ensure it fufills the requirements of the issue
• I have reviewed the 'files changed' and commented on any sections which I think are not needed, incorrect or could be improved

After pull

• If appropriate I have closed the issue/ moved the trello card