The styling of the pages generated by Remark is controlled
by two Cascading Style Sheet (CSS) files. They are
named remark.css and pygments.css. The generated pages
assume that these CSS files are found from the remark_files
sub-directory of the output directory. In case these files
are not found from the target directory during page generation,
default style-sheet files are copied there. The default CSS
files can be found from the remark_files sub-directory of the
Remark library. Changing the content of the CSS files (in the
target directory) allows you to change the representation of the
generated pages. The default remark.css file contains lots of
comments to get you quickly started on modifying the style to your
liking. After you have modified and saved a CSS file,
reload the page in your browser to see the changes.
Cascading Style Sheets at W3C is the official website of the CSS.
Cascading Style Sheets at Sitepoint is an excellent reference site for CSS.
CSS Zen garden is a demonstration of the abilities of CSS to completely change the look and feel of html.