CodePen

HTML

            
              
            
          
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CSS

            
              html {
  height: 100%;
  box-shadow: inset 0 0 0 106px white, inset 322px 0 0 white, inset -322px 0 0 white, inset 2000px 2000px 0 0 #0000ff;
}
            
          
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JS

            
              
            
          
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999px
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