Just like pseudo-classes, pseudo-elements are added to selectors but instead of describing a special state, they allow you to style certain parts of a document. For example, the ::first-line pseudo-element targets only the first line of an element specified by the selector.
The text-decoration CSS property is used to set the text formatting to underline, overline, line-through or blink. Underline and overline decorations are positioned under the text, line-through over it.
The CSS text-decoration-color property sets the line color used when drawing underlines, overlines, and strikethrough lines specified by the corresponding text-decoration-line property. The color specified will be the same for all three line types.
The text-decoration-style CSS property defines the style of the lines specified by text-decoration-line. The style applies to all lines, there is no way to define different style for each of the line defined by text-decoration-line.
The text-indent property specifies the amount of indentation (empty space) should be left before lines of text in a block. By default, this controls the indentation of only the first formatted line of the block, but the hanging and each-line keywords can be used to change this behavior.
The transition-timing-function CSS property is used to describe how the intermediate values of the CSS properties being affected by a transition effect are calculated. This in essence lets you establish an acceleration curve, so that the speed of the transition can vary over its duration.
The var() function can be used instead of any part of a value in any property on an element. The var() function can not be used as property names, selectors or anything else besides property values. (Doing so usually produces invalid syntax or else a value whose meaning has no connection to the variable.)