아코디언

var btns = document.querySelectorAll('.accordion');

  btns.forEach(function(btn){
  btn.addEventListener('click', function(){

  	this.classList.toggle('active');
	
    var pannel = this.nextElementSibiling;
    
    if(pannel.style.maxheight){
    	pannel.style.maxheight = null;
    } else {
    	pannel.style.maxheight = pannel.scrollheight + "px";
        
    }

})
})