Update background color of Left Menu components (both DragDropPanel and MUIDragDropPanel) to make consistent with background color of entire Left Menu

[johnwage]

Description

Please describe the issue of the pull request and the changes

• Update background color of Left Menu components (both DragDropPanel and MUIDragDropPanel) to make consistent with background color of entire Left Menu

Type of Change

Please check the options that apply

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has the Changes Been Tested?

• Visually tested through GUI and user experience.

Checklist:

• My code follows the style guidelines of this project
• Changes included in this pull request covers minimal topic
• I have performed a self-review of my code
• I have commented my code properly, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules