アニメーション

.scroll-fade-origin {
  opacity : 0;
  transform: translateY(-20px);
  transition: all 1s;
}
.scroll-fade {
  opacity : 0;
  transform: translateY(0px);
  transition: all 1s;
}

js

(function(){
    $(window).scroll(function (){
        $('.mask_animation').each(function(){
            var targetElement = $(this).offset().top;
            var scroll = $(window).scrollTop();
            var windowHeight = $(window).height();
            if (scroll > targetElement - windowHeight + 200){
              //$(this).find('.mask_inner').addClass('start');
              //$(this).addClass('start');
              //$(this).css('opacity','1');
              //$(this).css('transform','translate(-50%,-50%)');
              //$(this).css('transform','translateY(0)');
            }
        });
    });
});