The ::-ms-fill-upperCSSpseudo-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 greater than the value currently selected by the thumb.
The :any-linkCSSpseudo-class represents an element that acts as the source anchor of a hyperlink independent of whether it has been visited, that is, it matches every <a>, <area> or <link> elements with an href attribute. So, it matches all elements that match :link or :visited.
The :-moz-locale-dir(rtl)CSSpseudo-class matches an element if the user interface is being displayed right-to-left. This is determined by the preference intl.uidirection.locale (where locale is the current locale) being set to "rtl".
The backdrop-filter property provides for effects like blurring or color shifting the area behind an element, which can then be seen through that element by adjusting the element's transparency/opacity.
display-mode is a CSS media feature that selectively applies CSS based on the display mode of the application. This feature corresponds the Web app manifest's display member. Both apply to the top-level browsing context and any child browsing contexts. This query applies regardless of whether a web app manifest is present. Use this query to provide a consistant user experience between launching a site from an URL and lunching it from a desktop icon.
The CSS3 Flexible Box, or flexbox, is a layout mode providing for the arrangement of elements on a page such that the elements behave predictably when the page layout must accommodate different screen sizes and different display devices. For many applications, the flexible box model provides an improvement over the block model in that it does not use floats, nor do the flex container's margins collapse with the margins of its contents.
A media query consists of an optional media type and zero or more expressions that limit the style sheets' scope by using media features, such as width, height, and color. Media queries, added in CSS3, let the presentation of content be tailored to a specific range of output devices without having to change the content itself.