src/third_party/web_platform_tests/intersection-observer/empty-root-margin.html - cobalt - Git at Google

 <!DOCTYPE html>
 <meta name="viewport" content="width=device-width,initial-scale=1">
 <script src="/resources/testharness.js"></script>
 <script src="/resources/testharnessreport.js"></script>

 <style>
 #target {
   width: 100px;
   height: 100px;
   background-color: green;
 }
 </style>

 <div id="target"></div>

 <script>
 var target = document.getElementById("target");
 async_test((t) => {
     var observer = new IntersectionObserver(t.step_func_done((entries) => {
         var rootBounds = entries[0].rootBounds;
         assert_equals(rootBounds.left, 0);
         assert_equals(rootBounds.right, document.documentElement.clientWidth);
         assert_equals(rootBounds.top, 0);
         assert_equals(rootBounds.bottom, document.documentElement.clientHeight);
         observer.disconnect();
     }), { rootMargin: "" });
     observer.observe(document.getElementById("target"));
 }, "An empty rootMargin string is interpreted as a margin of size zero");
 </script>
	<!DOCTYPE html>
	<meta name="viewport" content="width=device-width,initial-scale=1">
	<script src="/resources/testharness.js"></script>
	<script src="/resources/testharnessreport.js"></script>

	<style>
	#target {
	width: 100px;
	height: 100px;
	background-color: green;
	}
	</style>

	<div id="target"></div>

	<script>
	var target = document.getElementById("target");
	async_test((t) => {
	var observer = new IntersectionObserver(t.step_func_done((entries) => {
	var rootBounds = entries[0].rootBounds;
	assert_equals(rootBounds.left, 0);
	assert_equals(rootBounds.right, document.documentElement.clientWidth);
	assert_equals(rootBounds.top, 0);
	assert_equals(rootBounds.bottom, document.documentElement.clientHeight);
	observer.disconnect();
	}), { rootMargin: "" });
	observer.observe(document.getElementById("target"));
	}, "An empty rootMargin string is interpreted as a margin of size zero");
	</script>