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<!DOCTYPE html>
<style>
.first:empty { color: blue; }
</style>
<script src="util.js"></script>
<script>
window.onload = function() {
let root = document.createElement("div");
let first = document.createElement("div");
first.className = "first";
first.appendChild(document.createElement("div"));
root.appendChild(first);
document.body.appendChild(root);
flush_style(root);
perf_start();
first.firstChild.remove();
flush_style(root);
perf_finish();
};
</script>