Color scheme

This is a very scratch version. Have three problems:
1. How to make persistent change of color scheme, shall I create a new model, and how should I sync to the server?
2. How to change another page's view from one page's view?
3. I find that the CSS files are very nested. Changing a color scheme means changes many CSS rules. Is there a way to handle this?
Steven, do you have any suggestions? Thank you!