The @charsetCSSat-rule specifies the character encoding used in the style sheet. It must be the first element in the style sheet and not be preceded by any character; as it is not a nested statement, it cannot be used inside conditional group at-rules. If several @charset at-rules are defined, only the first one is used, and it cannot be used inside a style attribute on an HTML element or inside the <style> element where the character set of the HTML page is relevant.
The@counter-styleCSSat-rule lets authors define specific counter styles that are not part of the predefined set of styles. A @counter-style rule defines how to convert a counter value into a string representation.
The @keyframes CSS at-rule lets authors control the intermediate steps in a CSS animation sequence by establishing keyframes (or waypoints) along the animation sequence that must be reached by certain points during the animation. This gives you more specific control over the intermediate steps of the animation sequence than you'd get when letting the browser handle everything automatically.
@namespace is an at-rule that defines XML namespaces to be used in a CSSstyle sheet. The defined namespaces can be used to restrict the universal, type, and attributeselectors to only select elements within that namespace. The @namespace rule is generally only useful when dealing with documents containing multiple namespaces—such as HTML5 with inline SVG or MathML, or XML that mixes multiple vocabularies.
The @page CSS at-rule is used to modify some CSS properties when printing a document.You can't change all CSS properties with @page. You can only change the margins, orphans, widows, and page breaks of the document. Attempts to change any other CSS properties will be ignored.
The CSS multi-column layout extends the block layout mode to allow the easy definition of multiple columns of text. People have trouble reading text if lines are too long; if it takes too long for the eyes to move from the end of the one line to the beginning of the next, they lose track of which line they were on. Therefore, to make maximum use of a large screen, authors should have limited-width columns of text placed side by side, just as newspapers do.
Specificity is the means by which browsers decide which CSS property values are the most relevant to an element and, therefore, will be applied. Specificity is based on the matching rules which are composed of CSS selectors of different sorts.
The CSSKeyframeRule interface describes an object representing a set of style for a given keyframe. It corresponds to the contains of a single keyframe of a @keyframesat-rule. It implements the CSSRule interface with a type value of 8 (CSSRule.KEYFRAME_RULE).
The CSSKeyframesRule interface describes an object representing a complete set of keyframes for a CSS animation. It corresponds to the contains of a whole @keyframesat-rule. It implements the CSSRule interface with a type value of 7 (CSSRule.KEYFRAMES_RULE).
Each element in the top layer's stack has a ::backdroppseudo-element. This pseudo-element is a box rendered immediately below the element (and above the element below the element in the stack, if any), within the same top layer.
The ::-ms-fill-lowerCSSpseudo-element represents the portion of the "track" (the groove in which the indicator aka thumb slides) of an <input> of type="range", which corresponds to values lower than the value currently selected by the thumb.