Fix inheritance.sub.html WPT to work on Servo
diff --git a/css/css-backgrounds/inheritance.sub.html b/css/css-backgrounds/inheritance.sub.html
index 01bb842..8af2dad 100644
--- a/css/css-backgrounds/inheritance.sub.html
+++ b/css/css-backgrounds/inheritance.sub.html
@@ -31,7 +31,7 @@
</style>
<script>
const transparentColor = 'rgba(0, 0, 0, 0)'; // https://www.w3.org/TR/css-color-3/#transparent
-const mediumWidth = getComputedStyle(document.getElementById('reference')).columnRuleWidth; // e.g. 3px
+const mediumWidth = '3px'; // https://www.w3.org/TR/css-backgrounds-3/#valdef-line-width-medium
const currentColor = 'rgb(2, 3, 4)';
container.style.color = currentColor;