style: Fixup the hack added in #18867.
style: Fixup the hack added in #18867.

The declaration can indeed have the same id if it contains variables, or is a
CSS keyword value.

This was making a WPT test fail, so this is tested, though Servo's WPT import
didn't catch this for some reason.

anthgur/servo,pyfisch/servo,KiChjang/servo,emilio/servo,jimberlage/servo,CJ8664/servo,jimberlage/servo,splav/servo,notriddle/servo,SimonSapin/servo,KiChjang/servo,jimberlage/servo,szeged/servo,jimberlage/servo,peterjoel/servo,dati91/servo,canaltinova/servo,thiagopnts/servo,nnethercote/servo,fiji-flo/servo,ConnorGBrewster/servo,mattnenterprise/servo,emilio/servo,dati91/servo,jimberlage/servo,canaltinova/servo,larsbergstrom/servo,cbrewster/servo,mattnenterprise/servo,dsandeephegde/servo,mbrubeck/servo,splav/servo,KiChjang/servo,SimonSapin/servo,KiChjang/servo,mattnenterprise/servo,notriddle/servo,emilio/servo,paulrouget/servo,rnestler/servo,larsbergstrom/servo,mbrubeck/servo,anthgur/servo,emilio/servo,fiji-flo/servo,avadacatavra/servo,SimonSapin/servo,mbrubeck/servo,notriddle/servo,dati91/servo,splav/servo,fiji-flo/servo,fiji-flo/servo,dsandeephegde/servo,eddyb/servo,jimberlage/servo,dsandeephegde/servo,upsuper/servo,szeged/servo,peterjoel/servo,upsuper/servo,szeged/servo,anthgur/servo,dati91/servo,larsbergstrom/servo,saneyuki/servo,larsbergstrom/servo,splav/servo,sadmansk/servo,DominoTree/servo,upsuper/servo,notriddle/servo,fiji-flo/servo,thiagopnts/servo,eddyb/servo,jimberlage/servo,CJ8664/servo,saneyuki/servo,rnestler/servo,pyfisch/servo,paulrouget/servo,peterjoel/servo,anthgur/servo,avadacatavra/servo,saneyuki/servo,DominoTree/servo,KiChjang/servo,fiji-flo/servo,notriddle/servo,anthgur/servo,DominoTree/servo,saneyuki/servo,cbrewster/servo,thiagopnts/servo,avadacatavra/servo,larsbergstrom/servo,sadmansk/servo,CJ8664/servo,rnestler/servo,DominoTree/servo,szeged/servo,emilio/servo,paulrouget/servo,pyfisch/servo,dsandeephegde/servo,canaltinova/servo,mbrubeck/servo,peterjoel/servo,sadmansk/servo,peterjoel/servo,rnestler/servo,ConnorGBrewster/servo,saneyuki/servo,splav/servo,avadacatavra/servo,splav/servo,jimberlage/servo,ConnorGBrewster/servo,mattnenterprise/servo,thiagopnts/servo,nnethercote/servo,notriddle/servo,szeged/servo,mattnenterprise/servo,pyfisch/servo,cbrewster/servo,nnethercote/servo,SimonSapin/servo,jimberlage/servo,mattnenterprise/servo,nnethercote/servo,upsuper/servo,KiChjang/servo,dati91/servo,CJ8664/servo,dati91/servo,rnestler/servo,larsbergstrom/servo,eddyb/servo,thiagopnts/servo,splav/servo,peterjoel/servo,peterjoel/servo,paulrouget/servo,dsandeephegde/servo,anthgur/servo,mattnenterprise/servo,saneyuki/servo,sadmansk/servo,anthgur/servo,rnestler/servo,CJ8664/servo,peterjoel/servo,DominoTree/servo,dsandeephegde/servo,KiChjang/servo,larsbergstrom/servo,larsbergstrom/servo,notriddle/servo,eddyb/servo,pyfisch/servo,pyfisch/servo,cbrewster/servo,CJ8664/servo,SimonSapin/servo,sadmansk/servo,paulrouget/servo,ConnorGBrewster/servo,ConnorGBrewster/servo,szeged/servo,saneyuki/servo,sadmansk/servo,saneyuki/servo,nnethercote/servo,SimonSapin/servo,fiji-flo/servo,peterjoel/servo,nnethercote/servo,ConnorGBrewster/servo,rnestler/servo,paulrouget/servo,mbrubeck/servo,notriddle/servo,sadmansk/servo,larsbergstrom/servo,cbrewster/servo,saneyuki/servo,rnestler/servo,upsuper/servo,DominoTree/servo,fiji-flo/servo,mbrubeck/servo,mbrubeck/servo,dati91/servo,pyfisch/servo,thiagopnts/servo,eddyb/servo,avadacatavra/servo,ConnorGBrewster/servo,thiagopnts/servo,DominoTree/servo,eddyb/servo,sadmansk/servo,eddyb/servo,emilio/servo,KiChjang/servo,thiagopnts/servo,dati91/servo,nnethercote/servo,saneyuki/servo,paulrouget/servo,peterjoel/servo,nnethercote/servo,splav/servo,szeged/servo,szeged/servo,pyfisch/servo,szeged/servo,eddyb/servo,canaltinova/servo,cbrewster/servo,canaltinova/servo,pyfisch/servo,KiChjang/servo,paulrouget/servo,DominoTree/servo,notriddle/servo,CJ8664/servo,dsandeephegde/servo,avadacatavra/servo,SimonSapin/servo,paulrouget/servo,avadacatavra/servo,upsuper/servo,canaltinova/servo,KiChjang/servo,nnethercote/servo,CJ8664/servo,mbrubeck/servo,notriddle/servo,emilio/servo,emilio/servo,canaltinova/servo,splav/servo,nnethercote/servo,ConnorGBrewster/servo,splav/servo,avadacatavra/servo,SimonSapin/servo,DominoTree/servo,pyfisch/servo,DominoTree/servo,canaltinova/servo,paulrouget/servo,mattnenterprise/servo,larsbergstrom/servo,emilio/servo,emilio/servo,cbrewster/servo,upsuper/servo,cbrewster/servo,anthgur/servo,dsandeephegde/servo,szeged/servo,upsuper/servo