The @documentCSSat-rule restricts the style rules contained within it based on the URL of the document. It is designed primarily for user style sheets. A @document rule can specify one or more matching functions. If any of the functions apply to a URL, the rule will take effect on that URL.
The @importCSSat-rule is used to import style rules from other style sheets. These rules must precede all other types of rules, except @charset rules; as it is not a nested statement, @import cannot be used inside conditional group at-rules.
The @mediaCSSat-rule associates a set of nested statements, in a CSS block that is delimited by curly braces, with a condition defined by a media query. The @media at-rule may be used not only at the top level of a CSS, but also inside any CSS conditional-group at-rule.
any-pointer is a CSS media feature that can be used to check whether any available input mechanism is a pointing device, and if so, how accurate it is.
overflow-inline is a CSS media feature which can be used to indicate whether content that overflows the viewport along the inline axis can be scrolled.
The width CSS descriptor is shorthand for setting both the min-width and the max-width of the viewport. By providing one viewport length value, that value will determine both the min-width and the max-width to the value provided.
The actual value of a CSS property is the used value after all approximations have been applied. For example, a user agent may only be able to render borders with a integer pixel value and may be forced to approximate the computed width of the border.
Browsers use the DOCTYPE declaration to choose whether to show the document using a mode that is more compatible with Web standards or with old browser bugs. Using a correct and modern DOCTYPE declaration at the start of your HTML will improve browser standards compliance.