How to make the site menu fixed?

Question

User navigation

I specify the following values ​​for classes in css styles:

position: fixed;
    left:0;
    top: 0;
    width: 100%;
    z-index: 999;
    max-width:0px;
    overflow:visible;
    background-color: #f69d01;
    margin: 0;
    transition: 0.25s ease-in;
    -webkit-transition: 0.25s ease-in;
    -moz-transition: 0.25s ease-in;
    -ms-transition: 0.25s ease-in;

the menu is not fixed when scrolling. menu code in html:

<section class="in_menu_wrapper ">
  <div class="container">
    <div class="row ">
      <div class="col-lg-3 col-md-3 col-sm-3 col-xs-6">
        <div class="in_logo ">
          <a href="index.html">
            <img src="images/logo.png" width="265" height="52" alt="">
          </a>
        </div>
      </div>
      <div class="col-lg-9 col-md-9 col-sm-9 col-xs-6">
        <nav class="navbar">
          <button type="button" class="navbar-toggle collapsed" data-toggle="collapse" data-target="#bs-example-navbar-collapse-1" aria-expanded="false">
            <span class="sr-only">Toggle navigation</span>
            <span class="icon-bar"></span>
            <span class="icon-bar"></span>
            <span class="icon-bar"></span>
          </button>
          
        
          <div class="collapse navbar-collapse" id="bs-example-navbar-collapse-1">
            <div class="in_menu nav navbar-nav">
              <ul>
                <li ><a href="index.html">Главная</a></li>
                <li ><a href="#company">О Нас</a></li>
                <li ><a href="#uslugi">Услуги</a></li>
                <li ><a href="#tarif">Тарифы</a></li>
                <li ><a href="#otziv">Отзывы</a></li>
                <li ><a href="#contactus">Контакты</a></li>
                
              </ul>
              
            </div>
          </div>
        </nav>
      </div>
    </div>
  </div>
</section>

Answer 1

take awaymax-width:0px;

$(function(){
    $(window).scroll(function() {
        if($(this).scrollTop() >= 66) {
            $('.in_menu_wrapper').addClass('stickytop');
        } else{
            $('.in_menu_wrapper').removeClass('stickytop');
        }
    });
});

.stickytop {
    position:fixed;
    top:0;
    z-index: 2;
}

Answer 2

almost figured it out, another position was indicated in another place, but now the block that was on top of the menu was blocked