Why should the overlay and spinner go to the beginning of the body?

  $(window).on('load', function(){

    $('.overlay, .spinner').fadeOut(800, function(){

      $('h1').fadeIn(100).css('transform', 'scale(1.4)');

    });
  });



//             <-----OCULTAR NAVEGACION----->
$(window).on('scroll', parallax);

let ultimoScroll = 0;

function parallax(){

  let scrollActual = $(window).scrollTop();

  if (scrollActual > ultimoScroll) {

    $('nav').addClass('oculto');

  } else {

    $('nav').removeClass('oculto');

  }
  ultimoScroll = scrollActual;
}


$(document).ready(function(){
  $('body').on('click', function(){

    let dataId   = $(this).data('id');
    let scroll   = $(window).scrollTop();
    let objetivo = $('#nosotros').offset().top;

    $('html').animate({
      scrollTop: objetivo
    },1000)

  });
});

/* ------------------ ESTILOS GENERALES ------------------*/
body {
  overflow-x: hidden !important;      /* no es necesario */
  overflow-y: scroll;                 /* no es necesario */
  font-family: "Montserrat",sans-serif;
  font-size: .95em;
  font-weight: 400;
  line-height: 23px;
  color: #8d8d8d;
  background-color: #fff;
}

li{
  list-style: none;
}

p {
  font-family: "Open Sans", sans-serif;
  font-size: 1.5em;
  font-weight: 400;
  line-height: 2em;
}

h1 {
  text-transform: uppercase;
  font-size: 5em;
  font-weight: 100;
  line-height: 1.313em;
  letter-spacing: 22px;
  font-family: 'Lato',sans-serif;
  color: black;
  margin-top: 240px;
  letter-spacing: 50px;
}


.spinner {
  position: absolute;
  height: 100px;
  width: 100px;
  border-top: 3px solid black;
  border-left: 3px solid black;
  border-right: 3px solid black;
  border-radius: 50%;
  top: 50%;
  left: 47%;
  animation: girar .4s linear 100;
}

@keyframes girar {
  0%{
    transform: rotate(0deg);
  }
  25%{
    transform: rotate(90deg);
  }
  50%{
    transform: rotate(180deg);
  }
  75%{
    transform: rotate(270deg);
  }
  100%{
    transform: rotate(360deg);
  }

}

.overlay{
  position:fixed;
  width:100%;
  height:100%;
  top:0;
  left:0;
  background:#BDBDBD;
  line-height: 100vh;
  text-align: center;
  font-size: 3em;
  /*display: none;*/
}

h2 {
  text-transform: uppercase;
  font-size: 1.4em;
  font-weight: 400;
  line-height: 1.53846em;
  letter-spacing: 1px;
}

h3 {
  text-transform: uppercase;
  font-size: 1.4em;
  font-weight: 400;
  line-height: 1.44444em;
  letter-spacing: 1px;
}

h5 {
  text-transform: uppercase;
  font-size: 1.5em;
  font-weight: 400;
  line-height: 1.44444em;
  letter-spacing: 1px;
}

.mano-alzada {
  text-transform: none !important;
  font-family: "Georgia",sans-serif;
  font-style: italic;
  font-weight: normal;
}

.boton {
  display: inline-block;
  padding: 7px 35px;
  text-transform: uppercase;
  font-size: 1.1em;
  letter-spacing: 2px;
}

.boton.oscuro {
  border: 1px solid #555;
  color: #fff;
  background-color: #111;
}

.boton.claro {
  border: 1px solid #ddd;
  color: #3f3f3f;
  background-color: #fcfcfc;
}

.boton.naranja {
  border: 1px solid #bd9f86;
  color: #000;
}

ul {
  padding-left: 0;
}


.padding-section {
  padding-top: 120px;
  padding-bottom: 120px;
}

.grey-section {
  background-color: rgb(245,245,245);
}

.devider {
  width: 20px;
  margin-bottom: 40px;
  border-bottom: 3px solid #bd9f86;
}

.subtitle {
  margin-bottom: 80px;
  font-family: "Georgia",sans-serif;
  font-size: 16px;
  font-style: italic;
  color: #333;
}

.subtitle i {
  margin-right: 10px;
  font-size: 1.5em;
}



.border-bottom {
  border-bottom: 1px solid #eee;
}

.divisor {
  width: 50px;
  height: 5px;
  margin: 10% auto 0;
  background-color: #d7d7d7;
}

.tachado {
  text-decoration: line-through;
}





/* ------------------ BARRA NAVEGACIÓN ------------------*/

nav {
  height: 72px;
  width: 100%;
  background: #FAFAFA;
  padding: 1px 0px;
  border-bottom: 1px solid #D8D8D8;
  border-top: 1px solid #D8D8D8;
  z-index: 900;
  transition: all .5s cubic-bezier(0.190, 0.585, 0.285, 0.865);
  position: fixed;
  top: 0;
  left: 0;
}

nav ul {
  float: right;
}

nav li {
  display: inline-block;
}

nav a {
  color: #555;
  text-transform: uppercase;
  letter-spacing: 2px;
  font-size: 1.5em;
  padding: 0 10px;
  display: block;
  line-height: 62px;
  margin: 5px 8px;
}

nav img {
  width: 60px;
  margin: 5px 10px;
  opacity: .8;
}




/* ------------------ SECCIÓN HERO ------------------*/

#hero {
  height: 100vh;
  background: rgba(0,0,0,0) url("../img/backgrounds/bg-header.jpg") no-repeat fixed center bottom / cover;
}

#hero p {
  text-transform: uppercase;
  font-family: "Lato",sans-serif;
  font-size: 1.3em;
  font-weight: 300;
}

#hero-noindex{
  padding:150px 0 230px;
}

#hero-noindex h1{
  font-size:4em;
  font-weight: 400;
  margin-bottom: 40px;
}

#hero-noindex ul li{
  display: inline-block;
  font-size: 1.2em;
  text-transform: uppercase;
}

#hero-noindex ul li a{
  color: grey;
}

#hero-noindex ul li::after{
  content: " / ";
  margin: 0 10px;
}

#hero-noindex ul li:last-of-type::after{
  content: "";
}





/* ------------------ INTRO NOSOTROS ------------------*/


#intro-nosotros {
  box-shadow: inset 0px 10px 20px rgba(0,0,0,.05);
}


#intro-nosotros p{
  text-align: justify;
  padding-right: 50px;
}

#intro-nosotros h2{
  font-family: "Georgia",sans-serif;
  font-size: 2.5em;
  text-align: center;
  text-transform: none;
  letter-spacing: 3px;
  margin-bottom: 100px;
  color: black;
}

#intro-nosotros .videoContainer{
  position: relative;
  overflow: hidden;
  padding: 0;
}

#intro-nosotros .videoControls {
  float: right;
}

#intro-nosotros .videoControls i::before {
  font-size: 21px;
}

#intro-nosotros #iconoPlayVid{
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  font-size: 9em;
  color: #444;
  cursor: pointer;
  z-index:500;
}

#intro-nosotros video{
  width: 100%;
}


#intro-nosotros .reveal {
  opacity: 0;
  transform: translateX(200px);
}


#intro-nosotros .reveal.visible {
  opacity: 1;
  transform: translateX(0px);
}




/* ------------------ SECCIÓN PROCESS ------------------*/

#process .facts {
  margin: 150px 0;
}

#process .numero {
  font-family: "Montserrat",sans-serif;
  font-size: 14em;
  font-weight: 400;
  letter-spacing: 2px;
  color: #edefeb;
}


.facts article {
  padding-left: 60px;
}




/* ------------------ SECCIÓN SKILLS ------------------*/

#skills {
  padding: 50px 0;
  background: rgba(0,0,0,0) url("../img/backgrounds/bg-skills.jpg") no-repeat fixed center top / cover;
}

#skills .elemento {
  padding: 20px;
  text-align: center;
  font-family: "Lato",sans-serif;
  font-weight: 300;
}

#skills .marco {
  padding: 20px;
  border: 1px solid white;
  background-color: rgba(255,255,255,0.1);
}


#skills .elemento h5 {
  margin-top: 20px;
  text-transform: lowercase;
  font-family: "Georgia",sans-serif;
  font-style: italic;
  color: #fff;
}

#skills i {
  margin-bottom: 40px;
  font-size: 4em;
  color: #fff;
}

#skills .numero {
  margin-bottom: 30px;
  font-family: "Montserrat",sans-serif;
  font-size: 42px;
  font-style: normal;
  font-weight: 400;
  color: #fff;
}



/* ------------------ SECCIÓN ABOUT ------------------*/

#about img {
  float: right;
  margin-top: 20px;
}

#about .claimCruz {
  margin-top: 20px;
  padding: 60px 20px;
  text-align: center;
  background: rgba(0,0,0,0) url("../img/graphic/contain-cross.png") no-repeat center / contain;
}

#about article {
  margin-top: 17px;
  margin-left: 30px;
  text-align: justify;
  line-height: 27px;
}

#about .boton {
  margin-top: 40px;
}



/* ------------------ SECCIÓN VIDEO ------------------*/

#video {
  position: relative;
  text-align: center;
  color: #fff;
  background: rgba(0,0,0,0) url("../img/backgrounds/bg-video.jpg") no-repeat fixed center top / cover;
}


#video .roller{
  position: absolute;
  width: 50%;
  height: 100%;
  right: 0;
  top: 0;
  background: url("../img/backgrounds/looping-blanco.png") no-repeat bottom right / contain;
}


#video h2 {
  margin-top: 20px;
  font-size: 3em;
  color: #fff;
}



#video i {
  font-size: 7em;
  color: white;
  cursor: pointer;
}



/* ------------------ SECCIÓN PROYECTOS ------------------*/

#proyectos {
  text-align: center;
  background: rgb(245,245,245) url('../img/backgrounds/looping-blanco.png') no-repeat scroll right bottom / cover;
}

#proyectos i {
  padding: 10px 20px 10px 10px;
  font-size: 32px;
  color: #bd9f86;
}

#proyectos .boton {
  margin-top: 60px;
}



/* ------------------ SECCIÓN SERVICIOS ------------------*/

#servicios article i {
  padding: 10px 20px 10px 10px;
  text-align: left;
  font-size: 32px;
  color: #bd9f86;
}

#servicios img {
  display: block;
  margin: 70px auto 40px;
  opacity: 0.3;
}






/* ------------------ HERO NOSOTROS ------------------*/

header.nosotros{
  background: rgba(0,0,0,0) url("../img/backgrounds/bg-nosotros.jpg") no-repeat fixed center top / cover;
}




/* ------------------ EQUIPO NOSOTROS ------------------*/

#team{
  position: relative;
}

#team article{
  text-align: center;
  position: relative;
}

#team article.visible {

  transform: translateY(0px);
  opacity: 1;
}


#team article img{
  margin-bottom: 30px;
}

#team article ul{
  position: absolute;
  top: 0;
  right: 0;
  font-size: 2em;
  background-color: white;
}

#team article ul .devider{
  width: 50%;
  margin: 0 25%;
  border-bottom: 1px solid #bd9f86;
  opacity: .5;
}

#team article ul li a{
  display: block;
  padding: 8px 15px;
  color: #bd9f86;
  font-size: .8em;
}

#team article header .devider{
  width: 50px;
  margin: 20px auto;
  border-bottom: 1px solid black;
  opacity: .2;
}

#team .row:last-of-type{
  margin-top: 100px;
}

#team .claimbar {
  background: rgba(0, 0, 0, 0) url("../img/graphic/contain-line.png") no-repeat scroll center center / contain ;
  margin-top: 20px;
  padding: 60px;
  text-align: center;
}

#team div[class^="progress"] {
  height: 4px;
  background: rgba(0,0,0,.2);
  margin-bottom: 10px;
  position: relative;
}

#team div[class^="progress"]:before {
  content: '';
  position: absolute;
  background:black;
  height: 100%;
  left:0;
  top:0;
  transition: width .8s;
}

#team .progress70:before{
  width:70%;
}

#team .progress100:before{
  width:100%;
}

#team .progress90:before{
  width:90%;
}

#team .progress50:before{
  width:50%;
}

#team > img{
  position: absolute;
  bottom: 0;
  right: 0;
  opacity: .04;
  z-index: -1;
}

/* ------------------ SECCIÓN TRABAJOS ------------------*/

#trabajos {
  padding-bottom: 0;
  padding-top: 0
}


#trabajos img {
  width: 100%;
  -webkit-filter: grayscale(80%);
  filter: grayscale(80%);
}

#trabajos .container-fluid,
#trabajos .row,
#trabajos div[class^="col-"] {
  margin: 0;
  padding: 0;
}


/* ------------------ EQUIPO TARIFAS ------------------*/

#rates article{
  text-align: center;
  background-color: #fff;
  padding: 30px 0 40px;
}

#rates .transparent {
  background-color: transparent;
  border: 2px solid #bd9f86;
}

#rates article header span{
  margin-bottom: 20px;
  display: block;
  font-size: 1.4em;
}

#rates article header h5{
  font-size: 1.8em;
  font-weight: bold;
  color: #555;
  letter-spacing: 3px;
}

#rates article .devider{
  width: 60%;
  margin: 20px 20%;
  border-bottom: 1px solid rgba(0,0,0,.2);
}

#rates article strong{
  margin: 40px 0;
  display: block;
  font-size: 2em;
  font-weight: bold;
  color: #555;
}

#rates article strong sup{
  font-size: .5em;
  vertical-align: middle;
  margin: 2px;
}

#rates article ul{
  margin-bottom: 40px;
}

#rates article ul .cross p{
  text-decoration: line-through;
  opacity: .5;
}

#rates article:not(.transparent) .boton{
  margin-bottom: 4px;
}


/* ------------------ SECCIÓN CONTACTO ------------------*/

#contacto {
  background: rgb(50,50,50) none repeat scroll 0 0;
}

#contacto * {
  color: white;
}

#contacto .form-control::-moz-placeholder {
  color: #000;
}

#contacto input:not(.boton),
#contacto textarea {
  width: 100%;
  margin-top: 25px;
  padding: 5px 20px 20px 14px;
  border-bottom: 1px solid #fff;
  text-transform: uppercase;
  font-family: "Lato",sans-serif;
  font-size: 1em;
  font-weight: 300;
  line-height: 1em;
  color: #fff;
}

#contacto .boton {
  float: right;
  margin-top: 40px;
}



/* ------------------ SECCIÓN FOOTER ------------------*/

footer {
  text-align: center;
  background: url("../img/backgrounds/bg-atracciones.png") no-repeat center bottom / cover;
}

footer h4 {
  margin-bottom: 40px;
}

footer a {
  color: #000;
}

footer .instagram li {
  display: inline-block;
  padding-right: 5px;
  padding-bottom: 10px;
  padding-left: 5px;
}

footer .sociales li {
  float: left;
}

footer address li{
  margin-bottom: 10px;
}


/* ------------------ MODAL ------------------*/

.modalVideo {
  z-index: 8000;
  width: 100%;
  height: 100%;
  background: rgba(0,0,0,.8);
  position: fixed;
  top: 0;
  left: 0;
  display: none;
}

.modalVideo video {
  display: block;
  max-width: 800px;
  margin: 50px auto;
}

.modalVideo h3 {
  color: white;
  text-align: center;
  font-size: 5em;
  margin: 50px 0;
}

.modalVideo .fa {
  color: white;
  font-size: 5em;
  position: fixed;
  margin: 20px;
  right: 0;
  top: 0;
  cursor: pointer
}

#alerta {
  background: #FAFAFA;
  position: fixed;
  bottom: 100px;
  left: 0;
  transition: all .5s;
  color: rgb(50,50,50);
  transform: translateX(-100%);
}

#alerta.visible{
  transform: translateX(0);
}

#alerta p {
  padding: 12px 10px;
  border: 2px dashed rgb(50,50,50);
  margin: 10px 35px;
  text-align: center;
  width: 300px;
  font-size: 14px;
  line-height: 16px
}

<!DOCTYPE html>
<html lang="es">
<head>
  <title>Central de ingredientes S.L</title>

  <!-- Descripcion en google -->
  <meta name="description" content="Desde 1994 somos tu proveedor de productos lácteos tanto nacional como internacional">

  <!-- Codificación -->
  <meta charset="utf-8">

  <!-- Estilos -->
  <link rel="stylesheet" type="text/css" href="css/font/flaticon.css">
  <link type="text/css" rel="stylesheet" href="css/bootstrap.min.css">
  <link rel="stylesheet" type="text/css" href="css/style.css">

  <!-- Responsive -->
  <meta name="viewport" content="width=device-width, initial-scale=1, user-scalable=yes">

  <!-- Robots -->
  <meta name="robots" content="index,follow">

  <!-- Favicones -->
  <link type="image/png" rel="icon" href="img/favicons/cow-512-231943.png">


</head>
<body>
  <div class="overlay">
    <div class="containerOverlay">
      <div class="spinner"></div>
      <p>Cargando...</p>
    </div>
  </div>
  <header id="hero">
    <div class="container">
      <div class="row">
        <div class="col-xs-12">
          <h1>Central de ingredientes</h1>
        </div>
      </div>
    </div>
  </header>
  <nav>
    <img src="img/cow_Logo.png" alt="Logo">
    <ul>
      <li><a href="#" class="menu" data-id="inicio">Inicio</a></li>
      <li><a href="#" class="menu" data-id="nosotros">Quienes somos</a></li>
      <li><a href="#" class="menu" data-id="productos">Productos</a></li>
      <li><a href="#" class="menu" data-id="calidad">Calidad</a></li>
      <li><a href="#" class="menu" data-id="logística">Logistica</a></li>
      <li><a href="#" class="menu" data-id="medio_ambiente">Medio ambiente</a></li>
      <li><a href="#" class="menu" data-id="contacto">Contacto</a></li>
    </ul>
  </nav>
  <main>
    <section id="nosotros" class="padding-extra">
      <div class="container">
        <div class="row">
          <div class="col-xl-12">
            <h2>Somos [central de ingredientes] desde 1994</h2>
            <hr>
          </div>
        </div>
        <div class="row">
          <div class="col-md-6">
            <p>Después de más de 20 años dedicado al sector lácteo, <span>central de ingredientes</span> se ha consolidado en el mercado, destacando tanto por su calidad, seriedad y confiabilidad en la fabricación tanto de preparados lácteos en polvo para chocolatería, como heladería o galletería. Incorporándose posteriormente al grupo su filial <span>Global blends ibérica</span></p>
            <div class="col-md-6">
            </div>
          </div>
          <div class="col-md-6">
            <img src="img/wallpapers/grey.jpg" alt="Photo">
          </div>

        </div>
      </div>
    </section>
  </main>
  <script  src="https://code.jquery.com/jquery-3.2.1.min.js"></script>
  <script src="js/app.js" charset="utf-8"></script>
</body>
</html>