I have made a command based on this page to run my build from the commandline with the dita toolkit. The build does run, but the style spedicifications are totally ignored. There is no error message about them, they just don't feature. My command is:
dita -i main.ditamap -f html5 -Dwebhelp.publishing.template=/mycomputer/mydirectory/publishing-template -Dwebhelp.publishing.template.descriptor=my_styles.opt -o out/ -d -l log.txt
my_styles.opt contains some images and css files for a colourscheme and things like font settings.
I have checked all of the paths and filenames, but the content always comes out plain.
These "webhelp.publishing.template" parameters are specific for imposing publishing templates for the commercial DITA to WebHelp Responsive outputs produced using the Oxygen XML plugins. Looking at the "-f html5" parameter, you are attempting to produce plain HTML5 output which does not use these parameters in any way. If you wanted to produce Oxygen WebHelp Responsive output you would need to specify the format parameter as "-f webhelp-responsive" but for this to work you would need the commercial Oxygen WebHelp responsive plugins installed in your DITA Open Toolkit.