The following rules must be followed:

• The CSS must be valid conform CSS 2.1 specification. This can be tested using the W3C validator
• don't hard code colors in proprieties - use ColorTheme attributes

The following recommendations could be followed:

• Proprieties:
  • alphabetical order;
  • 2 spaces indentation;
  • use of CSS shorthands;
  • use relative sizes (em, %) instead of fixed ones (px);
  • use appropriate CSS files for writing IE rules;
    • limit as much as possible the number of IE hacks used.

• Grouping:
  • comment headers for separation and grouping of different parts of the code;

• Overwriting Localization:
  • "Overwrites" and "Should be in"  comments for dependencies overwriting;