Full Idea
Hegel's disagreement with Kant is that categories are not unambiguously universal forms of human understanding, but are conceived in subtly different ways in different cultures and in different historical epochs.
Gist of Idea
Hegel said Kant's fixed categories actually vary with culture and era
Source
report of Georg W.F.Hegel (works [1812]) by Stephen Houlgate - Hegel p.95
Book Reference
'A Companion to Continental Philosophy', ed/tr. Critchley,S/Schroeder,W [Blackwell 1999], p.95
A Reaction
This may be Hegel's most influential idea. Though he hoped that categories would contain truth, by arising untrammelled from reason, and thereby matching reality. His successors seem to have given up on that hope, and settled for relativism.