task - translate: 'Kateřina je kost a kůže.' / your correct: 'Katerina is skin and bone.' / my correct but rejected: 'Katerina is bone and skin.'
It is an idiom https://www.macmillandictionary.com/dictionary/british/be-all-skin-and-bone-s
We may think about accepting it anyway...
Does "je kost a kůže" is an idiom in Czech? Or it can be "je kůže a kost" too?
"je kost a kůže" In that order, it is a Czech idiom.
... whose most accurate meaning in English is, by far, the English idiom "skin and bones"...
The German language has the same idom, meaning someone is very skinny.
It's an idiom.
You should! I am french speaking and not learning English here, but trying to learn Czech from English as it is not available from French.
Let's not pretend that "is bone and skin" is correct, though. It can be tolerated, but nothing this course can do will make it correct.
The correct phrase is skin and bones but I placed the words the other way around to be sure to get my points.
See nueby's answer.