Translation Question Again

Hello! Me the beginner in Latin come again.

A friend of me gave me some examples to translate to English like:
There is no one beautiful under the sky.
His answer is:
Est nemo pulchro sub caelo.

I don’t how to treat the adjective beautiful here. Why isn’t it pulchrum? And the content after “there be” structure in Latin still confuses me, especially its cases. Thanks for your help!

Your friend’s translation actually means: there is nobody under a beautiful sky.
Est nemo pulcher sub caelo.

pulcher, a, um is the adjective and nemo is masculine.