Hide all except first child of an element using pure css

Check out here https://jsfiddle.net/32vw04jg/1/

<div class="content">
  <div>
    <h3>abc</h3>
    <div class="classa">some content</div>
  </div>
  <div>
    <h3>xyz</h3>
    <div class="classa">more content</div>
  </div>
  <div>
    <h3>header3</h3>
    <div class="classa">another content</div>
  </div>
</div>


.content > div:not(:first-child) {
display: none;
}

If you want to support IE8, then your only option is general sibling selector:

div.classa ~ .classa {
    display: none;
}

<div class="content">
    <h3>abc</h3>
    <div class="classa">some content</div>
    <h3>xyz</h3>
    <div class="classa">more content</div>
    <h3>header3</h3>
    <div class="classa">another content</div>
</div>