"كُرْسي الْقِطّة غَريب."
Translation:The cat's chair is weird.
Because in the Arabic sentence above, the word غريب (strange/weird) is an adjective that has been used as a predicative (telling information) and not attributively to describe the cat's chair.
Your sentence would rather be: كرسي القطة الغريب (notice how the adjective now gets AL to be defined just like the noun composite كرسي القطة - these are 2 words bound together by a genitive relation (the chair of the cat/ the cat's chair) and since it is defined and I want to describe it, then the adjective has to be defined like the noun (attributive adjective follows the noun in its cases, gender, definition, and number). This is not the case above however, because the adjective had been used to TELL information (you can tell that by noticing the "is" in the English translation).