ladybird/Tests/LibWeb/Text/input/css/PropertyOwningCSSStyleDeclaration-serialized-custom-properties.html

<script src="../include.js"></script>
<script>
    test(() => {
        let styleNode = document.createElement("style");
        styleNode.innerText = `
            test {
                --color: red;
                color: red;
            }
        `;
        document.head.appendChild(styleNode);
        const sheet = styleNode.sheet;
        println(sheet.cssRules[0].cssText);
    });
</script>