Weekly Platform News: The :not() pseudo-class, Video Media Queries, clip-path: path() Support

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Hey, we’re back with weekly updates about the browser landscape from Šime Vidas.

In this week’s update, the CSS :not pseudo class can accept complex selectors, how to disable smooth scrolling when using “Find on page…” in Chrome, Safari’s support for there media attribute on <video> elements, and the long-awaited debut of the path() function for the CSS clip-path property.

Let’s jump into the news…

The enhanced :not() pseudo-class enables new kinds of powerful selectors

After a years-long wait, the enhanced :not() pseudo-class has finally shipped in Chrome and Firefox, and is now supported in all major browser engines. This new version of :not() accepts complex selectors and even entire selector lists.

For example, you can now select all <p> elements that are not contained within an <article> element.

/* select all <p>s that are descendants of <article> */
article p {

/* NEW! */
/* select all <p>s that are not descendants of <article> */
p:not(article *) {

In another example, you may want to select the first list item that does not have the hidden attribute (or any other attribute, for that matter). The best selector for this task would be :nth-child(1 of :not([hidden])), but the of notation is still only supported in Safari. Luckily, this unsupported selector can now be re-written using only the enhanced :not() pseudo-class.

/* select all non-hidden elements that are not preceded by a non-hidden sibling (i.e., select the first non-hidden child */
:not([hidden]):not(:not([hidden]) ~ :not([hidden])) {

The HTTP Refresh header can be an accessibility issue

The HTTP Refresh header (and equivalent HTML <meta> tag) is a very old and widely supported non-standard feature that instructs the browser to automatically and periodically reload the page after a given amount of time.

<!-- refresh page after 60 seconds -->

According to Google’s data, the <meta http-equiv="refresh"> tag is used by a whopping 2.8% of page loads in Chrome (down from 4% a year ago). All these websites risk failing several success criteria of the Web Content Accessibility Guidelines (WCAG):


However, WCAG does allow using the <meta http-equiv="refresh"> tag specifically with the value 0 to perform a client-side redirect in the case that the author does not control the server and hence cannot perform a proper HTTP redirect.

(via Stefan Judis)


CSS scroll-behavior: smooth is supported in Chrome and Firefox. When this declaration is set on the <html> element, the browser scrolls the page “in a smooth fashion.” This applies to navigations, the standard scrolling APIs (e.g., window.scrollTo({ top: 0 })), and scroll snapping operations (CSS Scroll Snap).

Unfortunately, Chrome erroneously keeps smooth scrolling enabled even when the user performs a text search on the page (“Find on page…” feature). Some people find this annoying. Until that is fixed, you can use Christian Schaefer’s clever CSS workaround that effectively disables smooth scrolling for the “Find on page…” feature only.

@keyframes smoothscroll1 {
  to {
    scroll-behavior: smooth;

@keyframes smoothscroll2 {
  to {
    scroll-behavior: smooth;

html {
  animation: smoothscroll1 1s;

html:focus-within {
  animation-name: smoothscroll2;
  scroll-behavior: smooth;

In the following demo, notice how clicking the links scrolls the page smoothly while searching for the words “top” and “bottom” scrolls the page instantly.

Safari still supports the media attribute on video sources

With the HTML <video> element, it is possible to declare multiple video sources of different MIME types and encodings. This allows websites to use more modern and efficient video formats in supporting browsers, while providing a fallback for other browsers.

  <source src="/flower.webm" type="video/webm">
  <source src="/flower.mp4" type="video/mp4">

In the past, browsers also supported the media attribute on video sources. For example, a web page could load a higher-resolution video if the user’s viewport exceeded a certain size.

  <source media="(min-width: 1200px)" src="/large.mp4" type="video/mp4">
  <source src="/small.mp4" type="video/mp4">


It is not appropriate for choosing between low resolution and high resolution because the environment can change (e.g., the user might fullscreen the video after it has begun loading and want high resolution). Also, bandwidth is not available in media queries, but even if it was, the user agent is in a better position to determine what is appropriate than the author.

Scott Jehl (Filament Group) argues that the removal of this feature was a mistake and that websites should be able to deliver responsive video sources using <video> alone.

For every video we embed in HTML, we’re stuck with the choice of serving source files that are potentially too large or small for many users’ devices … or resorting to more complicated server-side or scripted or third-party solutions to deliver a correct size.

Scott has written a proposal for the reintroduction of media in video <source> elements and is welcoming feedback.

The CSS clip-path: path() function ships in Chrome

It wasn’t mentioned in the latest “New in Chrome 88” article, but Chrome just shipped the path() function for the CSS clip-path property, which means that this feature is now supported in all three major browser engines (Safari, Firefox, and Chrome).

The path() function is defined in the CSS Shapes module, and it accepts an SVG path string. Chris calls this the ultimate syntax for the clip-path property because it can clip an element with “literally any shape.” For example, here’s a photo clipped with a heart shape: