CSS glossary entries for ‘V’

Valid selector: The valid selector (E:valid) is a CSS3 and CSS4 ‘pseudo-class selector’ which matches any <input> element whose content is valid for that input type. Its principal use is to update the styling of valid fields in dynamic forms, e.g. by rendering a green tick next to an input as soon as the user has correctly entered data into it.
Value: A CSS value is an optional setting for a CSS ‘property’. Each property has its own set of permitted values. Those values can be hyphen-separated keywords, integers, floating-point numbers, units of measurement, etc., depending on the property concerned. Values are typically terminated by semi-colons. Even though semi-colon ‘terminators’ are not always required CSS syntax, we recommend that you always use them.
vertical-align: The vertical-align property is a CSS property which specifies the vertical alignment of running text inside block boxes which are much larger than is necessary to tightly wrap the text. Its most common use case is for overriding the default middle alignment of text in table cells.
Viewport: In CSS, the viewport is the rectangular canvas on which a web page is drawn. On desktop computers it can be considered the browsers window's ‘work area’ and on most mobile devices it occupies the whole screen. It typically coincides with the screen area selected by the html ‘element type selector’ and often coincides with the area selected by body ‘element type selector’. Although it is not strictly an HTML element it is always treated by the browser as the ‘containing element’ of ‘fixed positioned’ elements and is also treated as the containing element for ‘absolutely positioned’ elements that have no non-static ancestors.
visibility: The visibility property is a CSS property which determines whether the content of a box is hidden from view. It has no effect on the visibility or otherwise of the containing box itself. Generally speaking, it only makes sense to use this property when you want to preserve a rectangle within the display, but only display its contents under certain conditions.
Visited hyperlink selector: See ‘visited link selector’
Visited link selector: The visited link selector (E:visited) is a CSS2 ‘pseudo-class selector’ which matches any link element whose target URL has been saved in the user's browser history. It is used primarily to let users know that a link points to content which they have already viewed previously. Distinctly styling visited links using the visited link selector is generally considered an essential feature of ‘website usability’. It is, however, widely over-looked by CSS designers.