HTML defines the document/page structure and lists the elements it contains. But the job of defining the layout, the positioning, and the styling of those elements is the sole responsibility of CSS. A cascading style sheet (CSS), as the name suggests, is basically a sheet that contains a list of style rules. Each CSS style rule links a selector, which defines what is going to be styled, to a declaration block, which includes a single or a set of styles, which in turn define the effect(s) you want applied to that associated selector. The syntax of a basic style rule would look like this

selector { property: value; property: value; }

Throughout this chapter, we will go over the following topics: CSS3 selectors, Grid and Flexbox, Animation and Transforms, and Media Queries. These topics cover some of the CSS3 features that are frequently used when developing a Windows Store app with JavaScript.