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HTML

            
              
            
          
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↑ Insert the most common viewport meta tag

CSS

            
              html {
  border: 200px solid white;
  padding-bottom: 30%;
  background: url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVQIW2NkYPj/HwADBwIAcbCYagAAAABJRU5ErkJggg==);
}
            
          
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JS

            
              
            
          
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