The system descriptor specifies the algorithm to be used for converting the integer value of a counter to a string representation. It is used in a @counter-style to define the behavior of the defined style.
The unicode-range CSS descriptor sets the specific range of characters to be used from a font defined by @font-face and made available for use on the current page. If the page doesn't use any character in this range, the font is not downloaded; if it uses at least one, the whole font is downloaded.
The @supportsCSSat-rule associates a set of nested statements, in a CSS block, that is delimited by curly braces, with a condition consisting of testing of CSS declarations, that is property-value pairs, combined with arbitrary conjunctions, disjunctions, and negations of them. Such a condition is called a supports condition.
The align-selfCSS property aligns flex items of the current flex line overriding the align-items value. If any of the flex item's cross-axis margin is set to auto, then align-self is ignored.
The animation-play-stateCSS property determines whether an animation is running or paused. This can be queried to determine whether or not the animation is currently running. In addition, its value can be set to pause and resume playback of an animation.
The background-position-x CSS property sets the initial horizontal position, relative to the background position layer defined by background-origin for each defined background image. For more information, see the background-position property, which has been widely supported.
The <basic-shape> type can be specified using basic shape functions. When using this syntax to define shapes, the reference box is defined by each property that uses <basic-shape> values. The coordinate system for the shape has its origin on the top-left corner of the reference box with the x-axis running to the right and the y-axis running downwards. All the lengths expressed in percentages are resolved from the used dimensions of the reference box.
The borderCSS property is a shorthand property for setting the individual border property values in a single place in the style sheet. border can be used to set the values for one or more of: border-width, border-style, border-color.