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HTML

            
              
            
          
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↑ Insert the most common viewport meta tag

CSS

            
              body {
  border: 10em solid yellow;
  margin: 0;
  width: 0;
  height: 0;
  position: absolute;
  top: 20%;
  left: 50%;
  margin-left: -10em;
  -webkit-filter: invert(100%);
  filter: invert(100%);
}

/* This may not work for FF/IE users */
            
          
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JS

            
              
            
          
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