Change background color posts and widgets

How do I change the background color of posts and widgets (text and non text)?

I have read several how-to’s and done what they said (I think) and the color never changes.

In the Appearance > Editor I have found several places where it says

body {
	background: #f1f1f1;

or similar and using https://www.quackit.com/css/css_color_codes.cfm I found the color code I want. I change the color and press “Update File” and check my page and nothing happens.

I also tried installing plug-ins but none seem to work and I’d rather learn how to do it in the Editor as it seems that will be more simple in the future.