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<html><head><style>#myDiv { border: 1px solid red; outline: dotted green;}</style></head><body><div id="myDiv" style="outline-width:10px;">This is a div element.</div><br><button type="button" onclick="myFunction()">Return outline width</button><script>function myFunction() { alert(document.getElementById("myDiv").style.outlineWidth);}</script></body></html>