On the standards track: Yes
Is Experimental: No
Is Deprecated: No
In Chrome version 129 on 2024-09-17 Note: When block-start is used as a single keyword, or alongside span-all, it unexpectedly allows the anchored box to overflow the viewport, obscuring content. Use place-self: anchor-center as a workaround. See bug 438334710.
In Chrome Android version 129 on 2024-09-17 Note: When block-start is used as a single keyword, or alongside span-all, it unexpectedly allows the anchored box to overflow the viewport, obscuring content. Use place-self: anchor-center as a workaround. See bug 438334710.
In Edge version 129 on 2024-09-19 Note: When block-start is used as a single keyword, or alongside span-all, it unexpectedly allows the anchored box to overflow the viewport, obscuring content. Use place-self: anchor-center as a workaround. See bug 438334710.
In Firefox version preview on undefined
Not in Firefox for Android
Not in Internet Explorer
Not in Quest Browser
In Opera version 115 on 2024-11-27 Note: When block-start is used as a single keyword, or alongside span-all, it unexpectedly allows the anchored box to overflow the viewport, obscuring content. Use place-self: anchor-center as a workaround. See bug 438334710.
In Opera Android version 86 on 2024-12-02 Note: When block-start is used as a single keyword, or alongside span-all, it unexpectedly allows the anchored box to overflow the viewport, obscuring content. Use place-self: anchor-center as a workaround. See bug 438334710.
In Safari version 26 on 2025-09-15
In Safari on iOS version 26 on 2025-09-15
In Samsung Internet version 28.0 on 2025-04-02 Note: When block-start is used as a single keyword, or alongside span-all, it unexpectedly allows the anchored box to overflow the viewport, obscuring content. Use place-self: anchor-center as a workaround. See bug 438334710.
In WebView Android version 129 on 2024-09-17 Note: When block-start is used as a single keyword, or alongside span-all, it unexpectedly allows the anchored box to overflow the viewport, obscuring content. Use place-self: anchor-center as a workaround. See bug 438334710.
In WebView on iOS version 26 on 2025-09-15