fix commonltr.css href in topics pages

[r-o-b]

All of the .html files in /topics/ have a 404 trying to load http://www.dita-for-small-teams.org/commonltr.css. It looks like you want to add the css folder to the path like this:
<link rel="stylesheet" type="text/css" href="../css/commonltr.css"></link>
(I would submit a pull request, but I'm not familiar with your processes in terms of what files are generated versus edited manually.)