[Deff]

<style type="text/css">
div {
 border:red solid 1px;
 width:130px;
 margin:2px;
 padding:6px;
}
#center {
 width:230px;
 height:40px;
 padding:6px;
 border:blue solid 1px;
}
</style>


<script type="text/javascript">
function change1() {
   var b = 'BLa-BLa-Текст для main';
   document.getElementById('center').innerHTML = b;
}
function change2() {
   var b= 'BLa-BLa-Текст для products';
   document.getElementById('center').innerHTML = b;
}
</script>


<div id="center"></div>

<br />
<br />

<div onclick="change1()" class="main"></div>
<div onclick="change2()" class="products"></div>