Heroku just recently made their ui styleguide/style kit public available. This is another great example of a good structured and visual appealing reference for the frontend elements. You provide code examples and actual design in this living document for typography, buttons, forms, grids, etc…
Such a reference can make a huge impact in terms of communication between different departments and stakeholders. Combine it with wireframes you get a really fast instrument to talk over and improve new design plans.
If not, don’t wonder if your end result is a design chaos, and your css/html is duplicated all over the place…