Hello,
Got to pages > Edit page > Page Layout > Page background
You can use custom CSS code. For example, add this code in Theme Options > Custom CSS area or in style.css file of child theme:
.shop-full-width {
background-color: hsla(0, 0%, 100%, 0.8);
}
Note, that you should not edit code in style.css of the parent theme.
Let us know if you need any further assistance.
Regards