change color in different position

Hi Daniel, again congratulations for your work, it s super!
I contact you because i want to change color default of minimatica.
In my site web [url=http://pizzadomiciliorimini.com/]pizzadomiciliorimini.com[/url], when you get on the homepage, you can see outside of sliding doors a black background. I tried to change the background color from the control panel of WP, but I don t found the solution. Maybe background is not a right term, I would like a light background, white.
I read every post on here on the forum, such as \”Change the size, police, and color of the blog title?\” , where advice to change the color values ​​in style.css, but I do not know where to operate. Any advice?
I hope I was sufficiently explicit.
Best regards an thank you very much for your work