doc/style: use default font color specified by user
* it's bad to specify only foreground color:
http://www.w3.org/QA/Tips/color
* some people prefer dark background
* `color: #111' is mostly the same as `color: black',
which is the default of almost all popular browsers.
so it's preferable to delete `color: #111', rather than adding
`background-color: white'.