need to fix the bootstrap navigation bar to fixed while scroll down - css

Question

I need to fix the below bootstrap code to fixed on the top of a web page while scrolling down. How can it do? please help me..
Here the bootstrap code that I have. Please help me to change this code from static to fixed while scrolling down the web page.
<div class="header_top" id="home">
<nav class="navbar navbar-expand-lg navbar-light bg-light">
<button class="navbar-toggler navbar-toggler-right mx-auto" type="button" data-toggle="collapse" data-target="#navbarSupportedContent"
aria-controls="navbarSupportedContent" aria-expanded="false" aria-label="Toggle navigation">
<span class="navbar-toggler-icon"></span>
</button>
<div class="collapse navbar-collapse" id="navbarSupportedContent">
<ul class="navbar-nav mx-auto">
<li class="nav-item active">
<a class="nav-link" href="index.html">Home
<span class="sr-only">(current)</span>
</a>
</li>
<li class="nav-item">
<a class="nav-link" href="about.html">About</a>
</li>
<li class="nav-item">
<a class="nav-link scroll" href="#menu">Menu</a>
</li>
<li class="nav-item">
<a class="nav-link" href="blog.html">Blog</a>
</li>
<li class="nav-item dropdown">
<a class="nav-link dropdown-toggle" href="#" id="navbarDropdown" role="button" data-toggle="dropdown" aria-haspopup="true"
aria-expanded="false">
Drop Down
</a>
<div class="dropdown-menu" aria-labelledby="navbarDropdown">
<a class="dropdown-item" href="#"></a>
<a class="dropdown-item" href="gallery.html">Gallery</a>
<div class="dropdown-divider"></div>
<a class="dropdown-item" href="404.html">Services</a>
</div>
</li>
<li class="nav-item">
<a class="nav-link" href="contact.html">Contact</a>
</li>
</ul>
</div>
</nav>
</div>

Answer 1

<nav class="navbar navbar-default navbar-fixed-top">
...
read this document for more details
https://getbootstrap.com/docs/3.3/components/#navbar-fixed-top

Answer 2

you can use css:
nav{
position: fixed;
}
actually what was written behind the class navbar-fixed-top

Answer 3

You can add:<nav class="navbar navbar-inverse" data-spy="affix" data-offset-top="197">
data-spy="affix" data-offset-fop="scroll amount"
You can see this link for example:
https://www.w3schools.com/bootstrap/tryit.asp?filename=trybs_affix&stacked=h
Another example: https://www.codeply.com/go/LDHQhWUG0x