You can use javascript to change the style of a div or any other element. But I donot know whether there is a way to change css by onclick event without using javascript.
I can explain my method.
<script>
function change_css(){
document.getElementById('change_css').className='newClassName';
}
</script>
<div onclick="change_css()" class="initial_class">content</div>
The above code will help you change the style by changing the class, provided you have already created a class with css. It replaces all the previously provided classes for that div and add the new one.
To add an additional class to the div without replacing the existing classes, use the following statement in javascript:
document.getElementById('change_css').className+=' newClassName';