1. CSS background-attachment

    Method of defining how a background image is attached to a scrollable element. Values include `scroll` (default), `fixed` and `local`.

  2. Background-clip: text

    Clipping a background image to the foreground text.

  3. CSS background-repeat round and space

    Allows CSS background images to be repeated without clipping.

  4. Background Sync API

    Provides one-off and periodic synchronization for Service Workers with an onsync event.

  5. CSS background-position edge offsets

    Allows CSS background images to be positioned relative to the specified edge using the 3 to 4 value syntax. For example: `background-position: right 5px bottom 5px;` for positioning 5px from the bottom-right corner.

  6. CSS Canvas Drawings

    Method of using HTML5 Canvas as a background image. Not currently part of any specification.

  7. CSS print-color-adjust

    The `print-color-adjust` (or `-webkit-print-color-adjust` as prefixed in WebKit/Blink browsers) property is a CSS extension that can be used to force printing of background colors and images.

  8. CSS currentColor value

    A CSS value that will apply the existing `color` value to other properties like `background-color`, etc.

  9. Resource Hints: dns-prefetch

    Gives a hint to the browser to perform a DNS lookup in the background to improve performance. This is indicated using `<link rel="dns-prefetch" href="https://example.com/">`

  10. Resource Hints: preconnect

    Gives a hint to the browser to begin the connection handshake (DNS, TCP, TLS) in the background to improve performance. This is indicated using `<link rel="preconnect" href="https://example-domain.com/">`

  11. Resource Hints: prerender

    Gives a hint to the browser to render the specified page in the background, speeding up page load if the user navigates to it. This is indicated using `<link rel="prerender" href="(url)">`

  12. CSS3 Multiple backgrounds

    Method of using multiple images as a background

  13. CSS3 object-fit/object-position

    Method of specifying how an object (image or video) should fit inside its box. object-fit options include "contain" (fit according to aspect ratio), "fill" (stretches object to fill) and "cover" (overflows box but maintains ratio), where object-position allows the object to be repositioned like background-image does.

  14. Service Workers

    Method that enables applications to take advantage of persistent background processing, including hooks to enable bootstrapping of web applications while offline.

  15. SVG in CSS backgrounds

    Method of using SVG images as CSS backgrounds

  16. Web Workers

    Method of running scripts in the background, isolated from the web page

  17. background-filter