html**
<script>
window.addEventListener('DOMContentLoaded', function (event) {
var scrollStart = $('.area01').offset().top;
var scrollEnd = $('.topics').offset().top;
var windowHeight = $(window).height();
var distance = 0;
$(document).scroll(function(){
distance = $(this).scrollTop();
console.log(distance);
console.log(scrollStart);
console.log(scrollEnd);
if (distance + windowHeight/2 < scrollStart || distance + windowHeight/2 > scrollEnd) {
$('.fix_square').fadeOut();
} else{
$('.fix_square').fadeIn();
}
});
});
</script>