Fix dark mode projects.scss colors - regression

What does this MR do and why?

Details mentioned in #239865 (comment 1605157055)

This MR fixes a regression caused by Import missing projects specific CSS on more li... (!131405 - merged). Even though the changes are behind an FF , the dark mode vars were left when moving to page_bundles projects.scss. The changes here will make sure that all colors are calculated according to the mixin depending on the mode.

Changelog: fixed

Screenshots or screen recordings

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Before	After

How to set up and validate locally

In addition to all paths being checked in the original MR , please check project detail page in both dark mode and light mode

Project detail page http://127.0.0.1:3000/flightjs/another-one-block-ror

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