Either an element zapper or a one click sticky-header killer should honestly be standard issue features in browsers nowadays. The web would be a miserable without them, especially on mobile.
In that case we could just match by the CSS rules' content - i.e. match all elements that have style X, Y, Z applied to them. That kind of arms race would be over real quick.
The arms race is that the next time you come back to the page, the offending element has a slightly different style (randomized CSS class name, RGB values changed by 1, font size changed by 0.1...) and your browser doesn't recognise it as being the right element to block.
