Do you want to change the whole widget area or just the background of each individual widget?
Try this and see if it is what you want:
.widget ul {
background-color: #f9f8ee;
}
To make changes to the theme you need to download the child theme and then activate it. (Instructions below.) Then you will be able to make your changes in the style.css folder.
You can download the child theme here by pressing the download Zip button. Then you go to Appearance => Themes => Install Themes Tab.
At the top of the screen choose the upload button. Browse on your computer for the zip file you just downloaded. Then press the Install Now button. Then activate your child theme.
First create an empty file in a text editor such as Notepad or TextEdit and name it style.css and put it in the leaf-child-master folder on your server.
Then you can go to the dashboard under Appearances => Editor and edit the child theme style.css. Just add the code above, refresh your page and see if it is the desired change you want.
Let me know if you have any questions.
