var faqItems = document.querySelectorAll('#faq .faq-item');
var faqItemsLength = faqItems.length;

function setMarginOffset(faqItem) {
    var answer = faqItem.querySelector('.answer');
    var height = answer.offsetHeight;
    answer.style.marginTop = (height * -1) + 'px';
    answer.style.opacity = 0;
}


for(var i = 0; i < faqItemsLength; i++){
    var faqItem = faqItems[i];

    faqItem.addEventListener('click', function () {
        this.classList.toggle('active');
    });
    setMarginOffset(faqItem);
}

window.onresize = function(event) {
    for(var i = 0; i < faqItemsLength; i++){
        var faqItem = faqItems[i];
        setMarginOffset(faqItem);
    }
};