Send me your store URL so I can check and assist you better.
Sorry this didn't help. I found the command in theme.scss.liquid but changes did not apply. The product site is https://lunashundeshop.de/collections/hundehalsbander/products/hundehalsband-handgefertigt-beauty-in...
Can you tell me which color you want to set in button? So according to it I will give you a solution.
If you are using debut theme, then you can simply go to the theme customization options and change it.
Under the customize section, you'll find the option under Theme Settings > Colors > Button
Refer to screenshot to know where to find it.
In case you want to change the color from the code side, then go to the css file, search for this hex code #2b2c7c. It should mostly be of your button only, change it to whatever color you would like.
Let me know if this helps.
ModeMagic - Product Labels (Shopify App)