css/css-variables/variable-reference-shorthands.html

<!DOCTYPE html>
<html>
<head>
    <title>Parse, store, and serialize CSS variable references - shorthand properties</title>

    <meta rel="author" title="Kevin Babbitt">
    <meta rel="author" title="Greg Whitworth">
    <link rel="author" title="Microsoft Corporation" href="http://microsoft.com" />
    <link rel="help" href="http://www.w3.org/TR/css-variables-1/#serializing-custom-props">

    <script src="/resources/testharness.js"></script>
    <script src="/resources/testharnessreport.js"></script>
</head>
<body>

<div id="target1" style="margin: var(--prop); margin-top: 10px"></div>
<div id="target2" style="margin: var(--prop) !important; margin-top: 10px"></div>
<div id="target3" style="margin: var(--prop); margin-top: 10px !important"></div>
<div id="target4" style="background: var(--prop);"></div>

<script type="text/javascript">
    "use strict";

    var testcases = [
        { element: "target1",   propertyName: "margin",         expectedPropertyValue: "" },
        { element: "target1",   propertyName: "margin-left",    expectedPropertyValue: "" },
        { element: "target1",   propertyName: "margin-top",     expectedPropertyValue: "10px" },
        { element: "target1",   propertyName: "margin-right",   expectedPropertyValue: "" },
        { element: "target1",   propertyName: "margin-bottom",  expectedPropertyValue: "" },

        { element: "target2",   propertyName: "margin",         expectedPropertyValue: "var(--prop)" },
        { element: "target2",   propertyName: "margin-left",    expectedPropertyValue: "" },
        { element: "target2",   propertyName: "margin-top",     expectedPropertyValue: "" },
        { element: "target2",   propertyName: "margin-right",   expectedPropertyValue: "" },
        { element: "target2",   propertyName: "margin-bottom",  expectedPropertyValue: "" },

        { element: "target3",   propertyName: "margin",         expectedPropertyValue: "" },
        { element: "target3",   propertyName: "margin-left",    expectedPropertyValue: "" },
        { element: "target3",   propertyName: "margin-top",     expectedPropertyValue: "10px" },
        { element: "target3",   propertyName: "margin-right",   expectedPropertyValue: "" },
        { element: "target3",   propertyName: "margin-bottom",  expectedPropertyValue: "" },

        { element: "target4",   propertyName: "background",     expectedPropertyValue: "var(--prop)" }
    ];

    testcases.forEach(function (testcase) {
        test( function () {
            var div = document.getElementById(testcase.element);
            var actualPropertyValue = div.style.getPropertyValue(testcase.propertyName).trim();
            assert_equals(actualPropertyValue, testcase.expectedPropertyValue);
        }, testcase.element + " " + testcase.propertyName);
    });
</script>

</body>
</html>