CSSG stands for “CSS Diagram”, in fact - a comment block in CSS file, which describes substance structure with CSS classes. Substance can be element, block or project, depending on methodology that you do (or do not) use.
This is your trusted companion in large project and assistant for your colleages, if you work in team.
Low entry barriers - use regular syntax and some logical rules.
However, it’s implied that you familiar with BEM, SMACSS, MCSS etc. and perhaps already use any of theese methodologies.
If not, you could possibly hear about Bootstrap and other frameworks.
Either way it is recommended to get yourself acquainted with OOCSS terminology before further reading.
For whom and for what
- Better code structure and getting into new code
- Conversation tool for colleages and developers, distant from front-end
- Detecting potential “bottlenecks” in layout (excessive DOM nesting, classes amount etc.)
- Easier debugging and refactoring
- It’s just pretty!
Of course it’s far more handy to get into into CSSG using automatic generator. Check out CSSG converter