CSS property

CSS property is an aspect of the element that you are choosing to style.

We will take background property as an example, so that you can understand how it works.

CSS background property

body {
    background: #00ff00 no-repeat fixed center;
} 

You can set all the background properties in one declaration. If you miss one of the elements like no-repeat, it will be not harmful to the rule itself.

Full list of CSS properties you can check in CSS Reference.