ads.js

<script>

var clsName = "selected"

var list = document.getElementsByTagName("p")


for (var i in list) {
    var el = list[i]
    el.addEventListener("click", function () {
    	if (el.classList.contains(clsName)) {
            el.classList.remove(clsName)
    	} else {
    	    el.classList.add(clsName)
    	}
    })
    
}
</script>

<style>
   

   .selected {
   background-color: ....
   ...
   }

</style>