Learn Swedish: Karins hatt är svart.

In Swedish, you show possession by adding an -s directly to the end of the owner's name, without an apostrophe. So, the English "Karin's" translates to Karins.

We are talking about a specific hat, so why do we use hatt instead of hatten (the hat)?

In Swedish, whenever a noun comes directly after an owner (like Karins), it must be in its basic, indefinite form. Saying Karins hatten is a common mistake for English speakers, but it is incorrect. The possessive name already makes it clear which hat we mean.

Why does the word for black (svart) not have an extra ending here?

Adjectives in Swedish must match the noun they describe. Because hatt is a singular en-word (en hatt), the adjective stays in its basic form: svart. If Karin had multiple hats, the adjective would take a plural ending and become svarta.