Referring to the original implementation of styles plugin
/libs/clientlibs/granite/coralui2/optional/rte/js/components/rte/plugins/StylesPlugin.js
Configs are taken from styles node in the rtePlugins config in component
Overlay this file, have a separate node structure outside component to maintain css styles the way you do in plugin config.
Change method getStyles in above file to read the values from you node structure based on the current page hierarchy