`::backdrop` CSS pseudo-element

The ::backdrop CSS pseudo-element is a box the size of the viewport, which is rendered immediately beneath any element being presented in the top layer.

Try it

button {
  font-size: 1.2rem;
  padding: 5px 15px;
}

dialog::backdrop {
  background-color: salmon;
}

<button id="showDialogBtn">Show a dialog</button>

<dialog id="favDialog">
  <form method="dialog">
    <p>The background shown outside of this dialog is a backdrop.</p>
    <button id="confirmBtn">Close the dialog</button>
  </form>
</dialog>

const showDialogBtn = document.getElementById("showDialogBtn");
const favDialog = document.getElementById("favDialog");

showDialogBtn.addEventListener("click", () => favDialog.showModal());

Syntax

::backdrop {
  /* ... */
}

Description

Backdrops appear in the following instances:

• Elements which have been placed in fullscreen mode using the Fullscreen API Element.requestFullscreen() method.
• <dialog> elements that have been shown in the top layer via a HTMLDialogElement.showModal() call.
• Popover elements that have been shown in the top layer via a HTMLElement.showPopover() call.

When multiple elements have been placed into the top layer, each one has its own ::backdrop pseudo-element.

/* Backdrop is only displayed when dialog is opened with dialog.showModal() */
dialog::backdrop {
  background: rgb(255 0 0 / 25%);
}

Elements are placed in a last-in/first out (LIFO) stack in the top layer. The ::backdrop pseudo-element makes it possible to obscure, style, or completely hide everything located below a top layer element.

::backdrop neither inherits from nor is inherited by any other elements. No restrictions are made on what properties apply to this pseudo-element.

Examples

Styling a modal dialog's backdrop

In this example, we use the ::backdrop pseudo-element to style the backdrop that is used when a modal <dialog> is open.

HTML

We include a <button> that, when clicked, will open the included <dialog>. When the <dialog> is opened, we give focus to the button that closes the dialog:

<dialog>
  <button autofocus>Close</button>
  <p>This modal dialog has a beautiful backdrop!</p>
</dialog>
<button>Show the dialog</button>

CSS

We add a background to the backdrop, creating a colorful donut using CSS gradients:

::backdrop {
  background-image:
    radial-gradient(
      circle,
      white 0 5vw,
      transparent 5vw 20vw,
      white 20vw 22.5vw,
      #eeeeee 22.5vw
    ),
    conic-gradient(
      #272b66 0 50grad,
      #2d559f 50grad 100grad,
      #9ac147 100grad 150grad,
      #639b47 150grad 200grad,
      #e1e23b 200grad 250grad,
      #f7941e 250grad 300grad,
      #662a6c 300grad 350grad,
      #9a1d34 350grad 400grad,
      #43a1cd 100grad 150grad,
      #ba3e2e
    );
}

JavaScript

The dialog is opened modally using the .showModal() method and closed using the .close() method.

const dialog = document.querySelector("dialog");
const showButton = document.querySelector("dialog + button");
const closeButton = document.querySelector("dialog button");

// "Show the dialog" button opens the dialog modally
showButton.addEventListener("click", () => {
  dialog.showModal();
});

// "Close" button closes the dialog
closeButton.addEventListener("click", () => {
  dialog.close();
});

Results

Specifications

Browser compatibility

See also

• :fullscreen
• :xr-overlay
• CSS positioned layout module
• CSS pseudo-elements module
• <dialog>
• popover HTML global attribute
• Fullscreen API
• Popover API