<html>
<head>
<style>
#myDiv {
border: thick solid blue;
}
</style>
</head>
<body>
<div id="myDiv">This is a div.</div>
<br>
<button type="button" onclick="myFunction()">Change color of the four borders</button>
<script>
function myFunction() {
document.getElementById("myDiv").style.borderColor = "green purple";
}
</script>
</body>
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</html>