CodePen

HTML

            
              <div>
  <p></p>
</div>
            
          
!

↑ Insert the most common viewport meta tag

CSS

            
              body {
  background: black;
}

div {
  width: 160px;
  height: 160px;
  background: white;
  text-align: center;
  margin: 0 auto;
  font-size: 32px;
  border-radius: 50%;
  -moz-border-radius: 50%;
  -webkit-border-radius: 50%;
}

p {
  padding-top: 24%;
}
            
          
!
? ?
? ?
Must be a valid URL.
+ add another resource
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JS

            
              var $winWidth = {
  width: $(window).width()
};

function removeOverlay() {
	if ( $winWidth.width < 768 ) {
		$('p').append(' (Narrow)');
    } else {
		$('p').append(' (Wide)');
	}
};

function getWidth() {
  $(window).bind( "resize", function ( event ) {
    var $this = $(this);
    $.each( $winWidth, function (key) {
      $winWidth[ key ] = $this[ key ]();
      $('p').text($winWidth.width + 'px');
    });
    removeOverlay();
  });
};

getWidth();
removeOverlay();
            
          
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Must be a valid URL.
+ add another resource
via JS Hint
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