Q:

CSS - Does there exist an opposite of “:inherit”

Is there an opposite of :inherit in CSS? ( If you are not familiar with :inherit: inherit)
E.g. to get an element to take over the width of its child, instead of its parent (the latter would be done using :inherit? 

A:

No, CSS was designed so that inheritance works only so that an element may inherit from its parent. 
The width of an element may depend on the widths of its children, but that’s an entirely different issue.  In some contexts, an element takes the minimum width needed to accommodate its children.  But that’s because it has been defined so; there is no magic word to use to achieve it in a manner comparable to the effect of the keyword inherit.