`::before` with `position: absolute` incorrectly positioned at viewport origin when parent element has zero size

[twhlynch]

Summary

When an element has no size (in my example, no content + inline positioning), it is positioned based on the viewport offset rather than its parent element.

Operating system

macOS

Steps to reproduce

Minimal snippet to reproduce the bug

<style>
    span {
        position: relative;
    }
    span::before {
        content: "c";
        position: absolute;
        top: 0;
        left: 0;
    }
</style>
a<span></span>b a<span> </span>b

The first span has no content and is zero size; the second has a space, making it non-zero-sized.

Expected behavior

The ::before element should be positioned based on its parent element, even when the parent has zero size.

Chrome places it where the element is

Actual behavior

The ::before element is placed at the viewport origin when the parent has zero size.

Ladybird places it at the viewport origin

URL for a reduced test case

https://refined-github-html-preview.kidonng.workers.dev/twhlynch/ladybird/raw/refs/heads/zero-size-parent-pseudo-element-positioning/Tests/LibWeb/Screenshot/input/css-zero-size-parent-with-pseudo-element.html

HTML/SVG/etc. source for a reduced test case

N/A

Log output and (if possible) backtrace

N/A

Screenshots or screen recordings

No response

Build flags or config settings

No response

Contribute a patch?

• I’ll contribute a patch for this myself.

[twhlynch]

To be clear, where I specify ::before, I mean both ::before and ::after pseudo-elements.