This is to set the location of the css stylesheet.
Previously it pointed to a path in the source directory.
By default, this was "./" so was okay as a location via HTTP.
But when built using a different source directory, then
the full source directory ended up as a reference on the webpage
so then style's didn't work.

I briefly discussed this on jabber yesterday but didn't get an okay.
It is a minor fix, so committing per my discretion.