This page what show you what their name is implies, selectors are used to specific HTML elements, that would stlyes by using different properties and to the corresonding values. A general syntax for this CSS rule(contain at least one selector and at least one property, and least one value.) is the following:
"selector {"
"property: value;"
"}"
Define/Explain Selectors and Properties
CSS properties are the styles used on specified selectors. They are written before values in the CSS ruleset and are separated from property values by a colon. Different HTML selectors and elements have different properties. Some properties are universal and can be used on every selector.
Document and Demo 4 selectors with a link to the reference page
Document and Demo 4 Properties with a link to the reference page