old_contents: $(document).ready(function(){
  	$('.js--article--next').mouseenter(function(){
  		$('.article--next').addClass('article--next--active');
  	});
  	$('.js--article--next').mouseleave(function(){
  		$('.article--next').removeClass('article--next--active');
  	});
  });
new_contents: $(document).ready(function(){
  	$('.js--article--next').mouseenter(function(){
  		$('.article--next').addClass('article--next--active');
  	});
  	$('.js--article--next').mouseleave(function(){
  		$('.article--next').removeClass('article--next--active');
  	});
  	$('.js--article--prev').mouseenter(function(){
  		$('.article--prev').addClass('article--prev--active');
  	});
  	$('.js--article--prev').mouseleave(function(){
  		$('.article--prev').removeClass('article--prev--active');
  	});
  });
subject: add same effect for prev button