"Those men are young and handsome."

[Salander_s]

Proč to přijímá "pěkný" a "hezký", ale "krásný" ne?

[Zygro]

Krásný = Beautiful

Krásný is a step above pěkný and hezký, something like beautiful is more than pretty and handsome.

[MrMorley3]

Can I not use "hezký" instead of "hezcí" here? Why not?

[Vixg]

Nope, "hezký" is for masculine singular, in this case "muži" is masculine animale plural and so it is "hezcí".
The grid will clarify all your doubts :)
https://en.wiktionary.org/wiki/hezk%C3%BD#Declension

[VladaFu]

As Vixg said. As a mnemotechnic aid you can also remember, that wherever you can use "ti", you use "hezcí, mladí, ...", where you use "ty", you use "hézké, mladé..." (děvče, město, stroje, stromy), with "ta" you have "hezká, mladá" (žena, děvčata)-

[Roberto247751]

Those men = ti muži
The men = ????

[BoneheadBass]

If you are asking what "the men" would be, it would also be ti muži.