<div class="wraper">
<h1 class="main_vsual">٩('ω')و</h1>
 <div class="nav_wrap">
   <nav>
     <ul>
       <li>list</li>
       <li>list</li>
       <li>list</li>
       <li>list</li>
     </ul>
   </nav>
 </div>
  <main>
    <div><img src="http://placekitten.com/300/300"> </div>
        <div><img src="http://placekitten.com/350/350"> </div>
        <div><img src="http://placekitten.com/800/800"> </div>
        <div><img src="http://placekitten.com/500/500"> </div>
        <div><img src="http://placekitten.com/700/700"> </div>
  
  </main>
  <footer>٩( ᐛ)و</footer>

</div>

.main_vsual{
  height: 150px;
  margin: 0;
  text-align: center;
  background-color: tomato;
  line-height: 150px;
  color:white;
  font-size: 50px;
}
.nav_wrap{
  height: 50px;
}
.nav_wrap nav{
  width: 100%;
  height: 50px;
  background-color: #5cb531;
}
.nav_wrap nav.fixed{
  position: fixed;
  top: 0;
  left: 0;
}

.nav_wrap nav ul{
  display: table;
  width: 100%;
  height: 100%;
}
.nav_wrap nav ul li{
  display: table-cell;
  vertical-align: middle;
  text-align: center;
  color: white;
  font-size: 18px;
  border: 1px solid #fff;
}
main{
  height: 1500px;
  text-align: center;
}
main div img{
  width: 300px;
  height: 300px;
  vertical-align: top;
}

footer{
  height: 50px;
  background-color: tomato;
  text-align: center;
  color: white;
  line-height: 50px;
}

var nav = $('.nav_wrap > nav'),
          offset = nav.offset();
      $(window).scroll(function () {
        if($(window).scrollTop() > offset.top) {
          nav.addClass('fixed');
        } else {
          nav.removeClass('fixed');
        }
      });