@Mega Completely fixed. used the plugin admin interface to uninstall (unbuild) every theme including lavender & vanilla.
Browsed to the node_module directory made sure all nodebb-theme-* were gone.
made sure I stopped the server
then did some 'npm install nodebb-theme-vanilla'
then 'npm install nodebb-theme-lavender'
start the server again then click theme in admin USE lavender and presto everything's back working
cheers, looks like a tonne easier adding your own Custom HTML/CSS, saves all your settings that way 👍