CodePen

HTML

            
              <div class="one">
  <ul>
    <li>One</li>
    <li>Two</li>
    <li>Three</li>
    <li>Four</li>
  </ul>
  <ol>
    <li>Five</li>
    <li>Six</li>  
    <li>Seven</li>
    <li>Eight</li>
  </ol>
  <i>select &lt;li&gt; elements that are the first child of their parent</i>
</div>

<div class="two">
  <ul>
    <li>One</li>
    <li>Two</li>
    <li>Three</li>
    <li>Four</li>
  </ul>
  <ol>
    <li>Five</li>
    <li>Six</li>
    <li>Seven</li>
    <li>Eight</li>
  </ol>
  <i>select the third child element of the second element</i>
</div>

<div class="three">
  <ul>
    <li>One</li>
    <li>Two</li>
    <li>Three</li>
    <li>Four</li>
  </ul>
  <ol>
    <li>Five</li>
    <li>Six</li>
    <li>Seven</li>
    <li>Eight</li>
  </ol>
  <ul>
    <li>Nine</li>
    <li>Ten</li>
    <li>Eleven</li>
    <li>Twelve</li>
  </ul>
  <i>select the first three &lt;li&gt; elements inside of every odd element</i>
</div>
            
          
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CSS

            
              body {
  padding: 1em 2em;
}

ul, ol {
  list-style: none;
  padding: 0;
}
li {
  text-align: center;
  line-height: 2;
  background: slategrey;
}
div {
  width: 12em;
  float: left;
  margin-right: 2em;
}
hr {
  clear: both;
  padding-top: 1em;
  border: 0;
  border-bottom: 1px solid grey;
}

.one li:nth-child(1) {
  background: lightsteelblue;
}

.two :nth-child(2) :nth-child(3) {
  background: lightsteelblue;
}

.three :nth-child(odd) li:nth-child(-n+3) {
  background: lightsteelblue;
}



div:before {
  font-family: monospace;
  white-space: nowrap;
  font-size: 12px;
}

.one:before {
  content: "li:nth-child(1)";
}
.two:before {
  content: ":nth-child(2) :nth-child(3)";
}
.three:before {
  content: ":nth-child(odd) li:nth-child(-n+3)";
}


            
          
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