[Webkit-unassigned] [Bug 279252] New: Feature detection starting styles

Fri Sep 6 02:02:38 PDT 2024

https://bugs.webkit.org/show_bug.cgi?id=279252

            Bug ID: 279252
           Summary: Feature detection starting styles
           Product: WebKit
           Version: Safari Technology Preview
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: CSS
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: imbashenk at hotmail.com
                CC: koivisto at iki.fi

Using the following method to detect if starting styles are available in the browser, does work in Chrome but doesn't work in Safari.

```
<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <title>Page Title</title>
  <meta name="viewport" content="width=device-width,initial-scale=1">
</head>

<body>
</body>
<style>
  @property --supported {
    syntax: "<number>";
    initial-value: 0;
    inherits: false;
  }

  :root {
    transition: --supported 0s calc(infinity * 1s);
  }

  @starting-style {
    :root {
      --supported: 1;
    }
  }

  body {
    background: red;
  }

  @container style(--supported: 1) {
    body {
      background: green;
    }
</style>

</html>

```

Live demo can be seen here: https://www.bram.us/2024/07/11/feature-detect-css-starting-style-support/

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