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HTML

            
              
            
          
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↑ Insert the most common viewport meta tag

CSS

            
              html { 
   width:100%; 
   height:100%; 
   background:url('http://upload.wikimedia.org/wikipedia/commons/5/5f/Blue_Box_in_museum.jpg') center center no-repeat;
}
            
          
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JS

            
              
            
          
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