How can I change the color of my 'add to cart' button?

[ihometech]

hi,
I wanted to change the color of my button "add to cart" but I can't. I've tried several codes that were left here but none work. I don't have any section called theme.css so I don't know if it's because of that. can you help me?

[ihometech]

Hi Peter,
Thanks for your answer but I couldn't find the file that contains the button... I looked everywhere.