fixes dropdown column select font color in bootstrap tables

[Godmartinz]

Description

The drop down menu in bootstrap tables column selectors was using var(--text-main) which was #FFF. I made a CSS rule for this drop down menu font to be #000 for all dark-mode themes. Also the Yellow dark-mode theme was still highlighter yellow, changed that as well.

Fixes # SC-19272

Type of change

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• [ X] Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

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• Test A
• Test B

Test Configuration:

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Checklist:

• I have read the Contributing documentation available here: https://snipe-it.readme.io/docs/contributing-overview
• I have formatted this PR according to the project guidelines: https://snipe-it.readme.io/docs/contributing-overview#pull-request-guidelines
• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, 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