Sorry, another page colour question!

Sorry, but I have a simple question about changing the page colour or body of my pages. I’m using a theme called Mantra, and I’ve just managed to create a child theme for it. Everything seemed to work, except the colour of my pages went from black to white. Mantra seems to have the option to change the colour of everything except the page background colour. I changed it before through trial and error in the css, but it took me ages, and I don’t fancy doing it again! Is there something that I can put in my child theme css that will overide the Mantra theme css?
my site is https://www.chrislewisdrums.co.uk
Thanks guys!