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 //volver arriba
    $(".back-top").click(function() {
      $("html, body").animate({
        scrollTop : "0px"
      });
      $(".back-top").stop().hide('fast');
    });
    
      var responsive_viewport = $(window).width();

  /* Boton scroll form */
  scrollPagina();

  function scrollPagina() {
    // ===== Scroll to Top ====
    $(window).scroll(function() {
      console.log(altura);
      if ($(this).scrollTop() >= altura) {        // If page is scrolled more than 50px
        mostrar();
      } else {
        ocultar();
        console.log('cerró');
      }
    });
  }
  function mostrar() {
    if (responsive_viewport < 768) {
      boton.slideDown(200);
    }
  }
  function ocultar(){
    if (responsive_viewport < 768) {
      boton.slideUp(200);
    }
  }