in assets/js/slick.js [2316:2417]
    Slick.prototype.setSlideClasses = function(index) {
        var _ = this,
            centerOffset, allSlides, indexOffset, remainder;
        allSlides = _.$slider
            .find('.slick-slide')
            .removeClass('slick-active slick-center slick-current')
            .attr('aria-hidden', 'true');
        _.$slides
            .eq(index)
            .addClass('slick-current');
        if (_.options.centerMode === true) {
            var evenCoef = _.options.slidesToShow % 2 === 0 ? 1 : 0;
            centerOffset = Math.floor(_.options.slidesToShow / 2);
            if (_.options.infinite === true) {
                if (index >= centerOffset && index <= (_.slideCount - 1) - centerOffset) {
                    _.$slides
                        .slice(index - centerOffset + evenCoef, index + centerOffset + 1)
                        .addClass('slick-active')
                        .attr('aria-hidden', 'false');
                } else {
                    indexOffset = _.options.slidesToShow + index;
                    allSlides
                        .slice(indexOffset - centerOffset + 1 + evenCoef, indexOffset + centerOffset + 2)
                        .addClass('slick-active')
                        .attr('aria-hidden', 'false');
                }
                if (index === 0) {
                    allSlides
                        .eq( _.options.slidesToShow + _.slideCount + 1 )
                        .addClass('slick-center');
                } else if (index === _.slideCount - 1) {
                    allSlides
                        .eq(_.options.slidesToShow)
                        .addClass('slick-center');
                }
            }
            _.$slides
                .eq(index)
                .addClass('slick-center');
        } else {
            if (index >= 0 && index <= (_.slideCount - _.options.slidesToShow)) {
                _.$slides
                    .slice(index, index + _.options.slidesToShow)
                    .addClass('slick-active')
                    .attr('aria-hidden', 'false');
            } else if (allSlides.length <= _.options.slidesToShow) {
                allSlides
                    .addClass('slick-active')
                    .attr('aria-hidden', 'false');
            } else {
                remainder = _.slideCount % _.options.slidesToShow;
                indexOffset = _.options.infinite === true ? _.options.slidesToShow + index : index;
                if (_.options.slidesToShow == _.options.slidesToScroll && (_.slideCount - index) < _.options.slidesToShow) {
                    allSlides
                        .slice(indexOffset - (_.options.slidesToShow - remainder), indexOffset + remainder)
                        .addClass('slick-active')
                        .attr('aria-hidden', 'false');
                } else {
                    allSlides
                        .slice(indexOffset, indexOffset + _.options.slidesToShow)
                        .addClass('slick-active')
                        .attr('aria-hidden', 'false');
                }
            }
        }
        if (_.options.lazyLoad === 'ondemand' || _.options.lazyLoad === 'anticipated') {
            _.lazyLoad();
        }
    };