CodePen

HTML

            
              <ul>
  <li class="diff"></li>
  <li class="diff"></li>
  <li class="diff"></li>
  <li class="diff"></li>
</ul>
            
          
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↑ Insert the most common viewport meta tag

CSS

            
              li{
  background: #CCC;
  border: 1px solid white;
  height: 100px;
}

.diff:nth-child(even){
  background: red;
}

            
          
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JS

            
              
            
          
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