CSS: Workaround to backdrop-filter?

Solution 1:

I use this to get the popular frosted glass effect. Until someone successfully invents a good polyfill for backdrop-filter I'm using a slightly transparent background as a fallback:

/* slightly transparent fallback */
.backdrop-blur {
  background-color: rgba(255, 255, 255, .9);
}

/* if backdrop support: very transparent and blurred */
@supports ((-webkit-backdrop-filter: none) or (backdrop-filter: none)) {
  .backdrop-blur {
    background-color: rgba(255, 255, 255, .5);
    -webkit-backdrop-filter: blur(2em);
    backdrop-filter: blur(2em);
  }
}

The filter will work in currently supported browsers. (Safari and Chrome with experimental Web Platform features enabled) The code should also work in future browsers that support unprefixed backdrop-filter if the spec doesn't change before that.

Examples without and with backdrop-filter support:

Solution 2:

Update as of 5/01/22:

Backdrop Filter has received further support, check the link for the versions of each browser that support it and a quick tutorial.

Syntax:

.element {
            backdrop-filter: <filter-function> [<filter-function>]* | none
         }

Older Solution

I don't know if you're still chasing this question, but for other users in future:

This effect can be accomplished as follows with CSS Pseudo-Classes, no JavaScript is necessary! shown below:

body,
main::before {
  background: url(https://s3-us-west-2.amazonaws.com/s.cdpn.io/80625/tree.jpg) 0 / cover fixed;
}

main {
  margin: 100px auto;
  position: relative;
  padding: 10px 5px;
  background: hsla(0, 0%, 100%, .3);
  font-size: 20px;
  font-family: 'Lora', serif;
  line-height: 1.5;
  border-radius: 10px;
  width: 60%;
  box-shadow: 5px 3px 30px black;
  overflow: hidden;
}

main::before {
  content: '';
  margin: -35px;
  position: absolute;
  top: 0;
  right: 0;
  bottom: 0;
  left: 0;
  filter: blur(20px);
  z-index: -1;
}

<main>
  <blockquote>"The more often we see the things around us &#45; even the beautiful and wonderful things &#45; the more they become invisible to us. That is why we often take for granted the beauty of this world: the flowers, the trees, the birds, the clouds &#45;
    even those we love. Because we see things so often, we see them less and less."
    <footer>&mdash;
      <cite>
        Joseph B. Wirthlin
      </cite>
    </footer>
  </blockquote>
</main>

Live example can be seen on Codepen: https://codepen.io/jonitrythall/pen/GJQBOp

Quick Note:

Depending on the structure of your HTML document, your z-indexes may be different to the one described in the example.

Solution 3:

As of Chrome M76, backdrop-filter is now shipped, unprefixed, and without a needed flag.

https://web.dev/backdrop-filter/

NOTE: (since this answer keeps getting downvoted because Mozilla hasn’t yet shipped it): this feature is available in Safari, Chrome, and Edge, but not yet in Firefox. Mozilla is planning to ship it very soon, but hasn’t yet. So this answer doesn’t contain a “workaround” but simply more information about which browsers require a workaround. Which still seems like useful information.

Solution 4:

Use SVG filters. They work like a charm. Checkout this example CodePen.

backdrop-filter is now supported by default in Chrome Canary. It's also in the 2019 priority list for Firefox development. So, it will soon be supported across all browsers, but for now you can use SVG filters.

Update

SVG filters don't work exactly like backdrop-filter. It's only a workaround and it doesn't work if there's moving elements beneath it. Anyway, I think we're going to be able to use backdrop-filter in production very soon. It's now enabled by default in Chrome Beta! Which also means Edge.