Untitled

<!DOCTYPE html>
<html>

  <head>
    <link rel="stylesheet" href="style.css">
    <script src="script.js"></script>
  </head>

  <body>
    <div class="target" style="display:none">test!!!</div>
    <input type="button" value="popup" onclick="window.open('popup.html','popup','width=400, height=200, menubar=no, status=no, toolbar=no');">
  </body>

</html>

// Code goes here

/* Styles go here */

<head>
<script data-require="jquery@3.1.1" data-semver="3.1.1" src="https://ajax.googleapis.com/ajax/libs/jquery/3.1.1/jquery.min.js"></script>
<script>
$(document).ready(function () {
	var targetValue = $('.target', opener.document).css('display');
  	
	if(targetValue == "none"){
		alert("ok!");
	}else{
	  alert("failed... => " + targetValue);
	}
});	
</script>
</head>
  <body>empty</body>
</html>