cleaning up CSS example code

I thought it might be nice to standardize a bit on how the CSS coded examples are presented, since there were some inconsistencies before. I made the following changes:

* For multi-line CSS examples, closing brackets are on their own line and not indented, e.g.:
  
  ```css
  body {
    color: black;
  }
  ```

* Final declarations in a CSS block have a terminating semicolon.
* Properties have a space after the colon.
* I used two spaces for indenting. (It looked like using spaces was the norm, but in some cases it was 3, not 2.)

In one instance (2.1.10), I also cleaned up some of the example HTML in an attempt to improve readability.

If another standard format would be preferable, let me know.