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<!DOCTYPE html>
<html>
<head>
<style>
::file-selector-button {
  border: 2px solid black;
  padding: 5px 10px;
  border-radius: 5px;
  background-color: lightgreen;
}
</style>
</head>
<body>
<h1>Demo of ::file-selector-button</h1>
<form>
  <label for="fileUpload">Upload file: </label>
  <input type="file" id="fileUpload" />
</form>
</body>
</html>