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<!DOCTYPE html>
<html>
<head>
<style>
body {
  background-color: #E7E9EB;
}
#myDIV {
  width: 100%;
  height: 300px;
  background-color: #FFFFFF;
  border-block-start-style: solid;
  border-block-start-width: thick;
}
</style>
</head>
<body>
<h1>The border-block-start-width Property</h1>
<div id="myDIV">
  A demonstration on different thicknesses of the border at the start in the block direction.
</div>
</body>
</html>