Seeing one of these error messages?
- set the body's "background-size" to "cover"
- expected body to have its background-position style equal to 50% 50% but got 0% 0%
- expected body to have its background-repeat style equal to no-repeat but got
- expected body to have its background-attachment style equal to fixed but got scroll
tl;dr : Put your background: url(' ....'); BEFORE any other background- properties.
For most of these CSS properties that we are learning about, the order in which you place them when you are building your code does not have any effect on the final appearance of your web page. BUT, there are some properties that are special, and where you place them does matter.
background is one of the special properties. It is shorthand property that can save you time, unless you don't know about its special power and then it will have you pulling your hair out.
background is a short form for several other related properties, some of which are important to us in this exercise. Your background: url(' ... '); line also sets the default values for these related properties. Here are four of these default values that will affect us:
background-position: 0% 0%
background-size: auto auto
If you place your background: url(' ....'); AFTER you have explicitly declared those properties then they will all be replaced by their default values. The exercise's code checker will now report your code as being incorrect.
More reading here, if you are interested.