I\'m sure this must have been mentioned/asked before but have been searching for an age with no luck, my terminology must be wrong!
I vaguely remember a twee
Any chance you're looking for the !important rule? It doesn't undo all declarations but it provides a way to override them.
"When an !important rule is used on a style declaration, this declaration overrides any other declaration made in the CSS, wherever it is in the declaration list. Although, !important has nothing to do with specificity."
https://developer.mozilla.org/en-US/docs/CSS/Specificity#The_!important_exception