The Potlatch 2 styles need to be patched in order to work with the JOSM MapCSS implementation. Potlatch 2's repository is git://git.openstreetmap.org/potlatch2.git * styles_nodist/potlatch2/source contains the unmodified source files copied from git.openstreetmap.org/potlatch2.git/history/master:/resources/stylesheets * styles_nodist/potlatch2/patched contains the manually edited version * images/icons copy of git.openstreetmap.org/potlatch2.git/tree/HEAD:/resources/icons * styles/standard/potlatch2.mapcss concatination of the patched files; the ant task 'assemble' helps with this (use build.xml in the current folder) When updating from upstream, keep all 4 locations in sync. At time of writing, the last update used 0a21b8bca71f6105c244cb52d7b7dcb5a840bd3a (2014-10-07) but better check the commit dates as well.