At-rules are CSS statements that instruct CSS how to behave.
Ref.: https://developer.mozilla.org/en-US/docs/Web/CSS/At-rule
media : String -> List CSS.Internal.Property -> CSS.Internal.Class -> CSS.Internal.Class
The @media CSS at-rule can be used to apply part of a style sheet based on the result of one or more media queries.
Ref.: https://developer.mozilla.org/en-US/docs/Web/CSS/@media