<style>
.korpus > div, .korpus > input { display: none; }

.korpus label { padding: 5px; border: 1px solid #aaa; line-height: 28px; cursor: pointer; position: relative; bottom: 1px; background: #fff; }
.korpus input[type="radio"]:checked + label { border-bottom: 2px solid #fff; }

.korpus > input:nth-of-type(1):checked ~ div:nth-of-type(1),
.korpus > input:nth-of-type(2):checked ~ div:nth-of-type(2),
.korpus > input:nth-of-type(3):checked ~ div:nth-of-type(3) { display: block; padding: 5px; border: 1px solid #aaa; }
</style>

<div class="korpus">
  <input type="radio" name="odin" checked="checked" id="vkl1"/><label for="vkl1">CSS</label><input type="radio" name="odin" id="vkl2"/><label for="vkl2">HTML</label><input type="radio" name="odin" id="vkl3"/><label for="vkl3">Дополнительно</label>
  <div>первая вкладка</div>
  <div>вторая вкладка</div>
  <div>третья вкладка</div>
</div>