CSS is a rule based, declarative language. Where you define rules for specified groups of HTML elements

h1 {
color: red font-size: 5em;

}

Terminology

Selectors are used to group html elements together to apply style to.

The inner box is 90% - 30px.

IDs must be unique for each HTML page.

Lorem ipsum dolor sit amet.

Lorem ipsum dolor sit amet.

Lorem ipsum dolor sit amet.