Contributions are very welcome and greatly appreciated! However, a few quick and simple guidelines for contributions:
If you don't like a particular color or style, that's fine - change it in your fork and make it your own. That's why this project is open source! But please don't submit issues or PRs just because you think some element should be a different shade of gray.
Important Note: This rule does not apply to all color changes, of course - color changes will be necessary after Rocket.Chat version updates or to improve readility or accessibility. Those changes are welcome.
Any code changes should work for all Rocket.Chat versions from the version used in the Rocket.Chat server snap (which is always a little behind) up to the lastest stable version available (within reason). When breaking changes are unavoidable, decisions will be made on a case-by-case basis. I (the repo owner) will do my best to discuss it with the community, but I reserve the right to make the final call for what goes into this repository.
However the code is already formatted, keep doing that. Use tabs (gasp! I know, I know) for indentation, various levels of comment styles to group CSS rules together, and new lines for each CSS selector in a rule. Beyond that, just make sure it looks clean. And please don't submit a PR to change tabs to spaces, etc.
I think this one's pretty self-explanatory. It covers the usual (don't be a jerk, don't insult or demean, etc.) but also includes good open source etiquette: make good, clean contributions to the community; don't abandon your PR or issue (or it will be closed); don't ask someone else to contribute what you can contribute yourself.