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HTML

            
              <div></div>

<input type="text">

<div>abc</div>

<input type="text" value="abc">
            
          
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↑ Insert the most common viewport meta tag

CSS

            
              :empty {
  border: 1px solid red; 
}

body {
  padding: 20px;
}
            
          
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JS

            
              
            
          
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