LayoutTests/fast/css/variables/redefinition.html

<script>
internals.settings.setCSSVariablesEnabled(true);
</script>
<style>
body {
    -webkit-var-a: red;
}
#a {
    -webkit-var-a: green;
}
#b {
    -webkit-var-a: blue;
}
div {
    color: -webkit-var(a);
}
</style>
<div>
This text should be red.
</div>
<div id="a">
This text should be green.
</div>
<div id="b">
This text should be blue.
</div>