The :disabled pseudo-class selector provides conditional styling to HTML elements that can receive user input, when the elements have the disabled attribute.
It is defined in the CSS Selectors Level 3 spec as a “UI element state pseudo-class”, meaning it is used to style content based on the user’s interaction with an input element.
Elements that can receive the disabled attribute include button, input, textarea, optgroup, option and fieldset.
There are two valid syntaxes for setting this attribute: either disabled=”disabled” or (in HTML5) simply the disabled Boolean keyword. An element is disabled if it can’t be activated (e.g. selected, clicked on or accept text input) or accept focus. Such an element can be styled using the :disabled pseudo-class selector.