fix: updated the background on attribute dropdown in fast tooling used in component explorer

[khamudom]

Description

Created a new css property called FloatingCSSProperty with the color of #3b3b3b. This is applied to the option in the select input dropdown. This fixes the issue where the background in the dropdown blends into the background of the pane.

closes #3979

before

after

Motivation & context

Issue type checklist

• Chore: A change that does not impact distributed packages.
• Bug fix: A change that fixes an issue, link to the issue above.
• New feature: A change that adds functionality.

Is this a breaking change?

• This change causes current functionality to break.

Adding or modifying component(s) in @microsoft/fast-components checklist

• I have added a new component
• I have modified an existing component
• I have updated the definition file
• I have updated the configuration file

Process & policy checklist

• I have added tests for my changes.
• I have tested my changes.
• I have updated the project documentation to reflect my changes.
• I have read the CONTRIBUTING documentation and followed the standards for this project.

[janechu]

As an addition to our manual testing, can you add something to the CSSPropertyOverrides in app/pages/form.tsx around line 80?

[SethDonohue]

Is there a reason for the vague name? Seems like it would be hard to decipher what it is used for.

[khamudom]

Is there a reason for the vague name? Seems like it would be hard to decipher what it is used for.

It was suggested by Brian