Hi well done for this challenge.
You have a problem between 600px and 1200px.
@media only screen and (min-width: 1200px)
@media only screen and (max-width: 600px)
You don't set any css between both.
It's better to start your css by mobile approach and then you set with media screen
desktop version
freecodecamp.
And for github just click 'new' when you want to edit a new website with only file of this website. After it's a mess to find what you want.
Hope to be helpful.