ser1ko,
<!DOCTYPE html>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
.class1 {
color: #008000;
}
.class2 {
color: #FF0000;
font-size: 48px;
}
</style>
<script>
document.addEventListener('click', function({target}){
if (target = target.closest('.class1')) {
target.classList.remove('class1')
target.classList.add('class2')
} else if (target = document.querySelector('.class2')) {
target.classList.remove('class2')
target.classList.add('class1')
}
})
</script>
</head>
<body>
<div class="class1">
здесь текст
</div>
</body>
</html>