The universal pronoun (każdy, każda, każde)

Każdy Declines Like an Adjective

You have used każdy since lesson 141 — now the whole paradigm. It takes ordinary adjectival endings, agreeing with its noun in gender and case:

The Genitive of Time

Każdego dnia, każdego ranka, każdej zimy — the Genitive marks the repeated time frame, exactly like pewnego dnia.

No Plural of Its Own

Każdy is singular-only: każdy uczeń — every pupil, one at a time. For the whole group Polish switches to wszyscy / wszystkie, which you know from lesson 9.