u/BusyLocksmith6463

hey guys, I'm new in the music theory and I just composed a melody with the chords D#7, Dm7 and C7, but when I look on a website, it tells me that it's in the scale Cmajor (so C, D, F, G, A, B), so why my D#7 sounds good with the rest? he is not in the scale so I don't know why.

I learned also the music "my song" by labi siffre, and there is only white notes in the song (it is in the scale Cmajor), and at a moment he plays a F#, and I don't know why it sounds good because this note is not in the scale . Can I have informations about this please?