White line padding issue between header/nav HTML CSS

Question

Here's what I'm seeing

I've tried removing the margins/padding from nav, header, li, body, head, and html, and it didn't work. I tried to post my HTML but it's too long apparently. Any help/suggestions would be great, thank you!

h1 {
 background:yellow;
}

<link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.5.2/css/bootstrap.min.css">
    <header>
        <h1 class="pt-2 pl-4 pb-2">ExampleSite.net</h1>
    </header>

    <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" data-toggle="collapse" data-target="#collapse_target">
                <span class="navbar-toggler-icon"></span>
            </button>

            <div class="collapse navbar-collapse" id=collapse_target>
                <ul class="navbar-nav">
                    <li class="nav-item">
                        <a class="nav-link" href="#">Link 1</a>
                    </li>
                    <li class="nav-item">
                        <a class="nav-link" href="#">Link 2</a>
                    </li>
                    <li class="nav-item">
                        <a class="nav-link" href="#">Link 3</a>
                    </li>
                    <li class="nav-item">
                        <a class="nav-link" href="#">Link 4</a>
                    </li>
                </ul>
            </div>
        </div>
    </nav>