# Backdrop The backdrop component can be used as background to obscure the content behind modal user interface elements, such as a modal dialog. ## Terminology "Backdrop" matches the name for the `::backdrop` CSS pseudo-element selector of the HTML element `dialog`. "Viewport" matches the name of the containing block for [`position: fixed`](https://drafts.csswg.org/css-position/#valdef-position-fixed) in CSS.