Change css dynamicaly using javascript

I have defined two classes namely first,second to define the styles of the div. These classes get interchanged by simply clicking on the done. This functionality is achieved by the javascript function. The two css classes look like .

.first{
background:silver;
padding:20px;
color:#ffffff;
}
 
.second{
background:yellow;
padding:30px;
color:#000000; 
}

Now we need to define the logic in javascript which let us interchange the two classes dynamically.

function changeClass(x)
{
x.className=(x.className=="first")?"second":(x.className=="second")?"first":"second";

}