Why doesn't sticky-top work?

Question

css

I work with BS4, everything is fine, but sticky-top refuses to work. I've been butting with him for an hour now, I can't figure out what the problem could be. A piece of code with a bar

<section>   
       <div class="mhead">
    <img src="img/top2.png" class="img-fluid">
</div>
</section>        
  <nav class="navbar navbar-expand-md navbar-dark bg-dark sticky-top">
      <div class="container-fluid">
    <a class="navbar-brand" href="#"></a>
    <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarCollapse" aria-controls="navbarCollapse" aria-expanded="false" aria-label="Toggle navigation">
      <span class="navbar-toggler-icon"></span>
    </button>
    <div class="collapse navbar-collapse" id="navbarCollapse">
      <ul class="navbar-nav mr-auto navbar-center">
        <li class="nav-item active">
          <a class="nav-link" href="/index.html">Главная <span class="sr-only">(current)</span></a>
        </li>

Screenshot

Answer 1

The sticky-top element needs to be a direct child of the container being scrolled (most likely your body ).