I have an array 

```
var arr = [2,5,8,11,14,17,....];

```

Use this array we have to apply css background for li elements

Html:

```
      <ul>
     <li>testing</li>
     <li>testing</li> // -->2nd li be green 
     <li>testing</li>
     <li>testing</li>
     <li>testing</li> // -->5th li be green
     <li>testing</li>
     <li>testing</li>
     <li>testing</li> // -->8th li green like this
     <li>testing</li>
     <li>testing</li>
     <li>testing</li>
     <li>testing</li>
     <li>testing</li> 
    <li>testing</li>
</ul>

```

I tried 

```
ul li:nth-child(2n + 2){

       color: green;
  }

```

Any Help???