This chapter introduces CSS. Whereas the last ones focused solely on HTML. Basically, you use CSS to style/design how you want your page to look. In CSS you write rules for html elements, these rules dictate how you want to style elements. Each rule is made of a selector (which indicates what elements the rule applies to) and a declaration (which indicates how the element should be styled). Declarations are made up of properties (which indicates the aspect of the element you want to change, for example, color) and a value (which indicates the specific setting for the property, for example, yellow).
I wrote all this down in my notes below but I thought it was important so I re-wrote it here.
Also, here is a website that has a list of CSS selectors.
Chapter 10 webpage notes
Chapter 10 code notes