changing text background colour Twenty Eleven theme

hellow again, am customizing the child theme of my blog one step at a time.

I’m currently using the ‘light’ theme and have easily changed the main background colour to white using the dashboard menu. However I’ve noticed that all the areas which I’ve written on has grey background colour (in the current website i’ve written on the ‘about’ and ‘say hello’ page.

How do I change all text area background colour to white in my childtheme?

TIA