Best way to "switch" 2 or more css libraries/files potentially colliding used in 2 states/routes ?

Let's say I have 2 parts of a bigger website that typically look a lot different from the main website, ...like totally different and using totally different CSS assets (for historical reasons, etc.). When loading those 2 parts, I dont want them to "overwrite" neither any style from -a) the main site itself; & -b) nor each other.

Just to be sure, the way to deal with this is indeed with help from this cool plugin to specifically load the css needed WHEN I arrive on this $state (ui-router) and (also?) unload any "main" css files from the main websiite potentially colliding with the new css ...and when leaving to "reload" the "old" css from the main files and "unload" the css from $state I was on ? (And repeat same thing for the second 'special' part from my exampe)

Am I correct ? Thanks a lot.