I never know when shall I use: "varm" or "varmt"
'varm' is for masculine/feminine, 'varmt' is for neuter. 'det' is neuter in this case, so you should use 'varmt'.
Thanks. I was trying to match the gender of dyna by mistake
Dynen is feminine? If so, why does "varm" have a "t"?
As mentioned above, it is agreeing with the neuter "det"
In this case "warm" is an adverb not an adjective
I have to disagree. It is an adjective modifying the pronoun "det".
Dyne eller dyna?
You can say dynen, as a masculine noun = en dyne, dynen, flere dyner, dynene.
Dyna. It is the definite form of the feminine noun, ei dyne.