Buttons are non living so shouldn't it be kurz instead of klein?
„kurz“ means “short”, not “small”.
Why is it Die here but Der when youre trying to say the button?
(der) Knopf is a masculine noun.
Here, you have the word in plural nominative for which the article is die.
Plural words always go to "Die"
The gender of the word Knopf is Der.
So der Knopf - Die Knöpfen
The button - the buttons.
"der" is not the gender, but the definite article used for a masculine (that's the gender) noun in nominative case singular.
Der Knopf (Einzahl)
Die Knöpfe (Mehrzahl)
I related Der Knopf with the knob and it is easy to remember this way.