Взял с бутстрапа оффканвас навбар. выглядит это все так:
<!DOCTYPE html>
<html lang="ru">
<head>
<link href="https://cdn.jsdelivr.net/npm/bootstrap@5.3.0/dist/css/bootstrap.min.css" rel="stylesheet" integrity="sha384-9ndCyUaIbzAi2FUVXJi0CjmCapSmO7SnpJef0486qhLnuZ2cdeRhO02iuK6FUUVM" crossorigin="anonymous">
<link rel = "stylesheet" href= "style.css"></link>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>???</title>
</head>
<body>
<header>
<nav class="navbar navbar-dark bg-dark fixed-top">
<div class="container-fluid">
<a class="navbar-brand" href="#">Offcanvas dark navbar</a>
<button class="navbar-toggler" type="button" data-bs-toggle="offcanvas" data-bs-target="#offcanvasDarkNavbar" aria-controls="offcanvasDarkNavbar" aria-label="Toggle navigation">
<span class="navbar-toggler-icon"></span>
</button>
<div class="offcanvas offcanvas-end text-bg-dark" tabindex="-1" id="offcanvasDarkNavbar" aria-labelledby="offcanvasDarkNavbarLabel">
<div class="offcanvas-header">
<h5 class="offcanvas-title" id="offcanvasDarkNavbarLabel">Dark offcanvas</h5>
<button type="button" class="btn-close btn-close-white" data-bs-dismiss="offcanvas" aria-label="Close"></button>
</div>
<div class="offcanvas-body">
<ul class="navbar-nav justify-content-end flex-grow-1 pe-3">
<li class="nav-item">
<a class="nav-link active" aria-current="page" href="#">Home</a>
</li>
<li class="nav-item">
<a class="nav-link" href="#">Link</a>
</li>
<li class="nav-item dropdown">
<a class="nav-link dropdown-toggle" href="#" role="button" data-bs-toggle="dropdown" aria-expanded="false">
Dropdown
</a>
<ul class="dropdown-menu dropdown-menu-dark">
<li><a class="dropdown-item" href="#">Action</a></li>
<li><a class="dropdown-item" href="#">Another action</a></li>
<li>
<hr class="dropdown-divider">
</li>
<li><a class="dropdown-item" href="#">Something else here</a></li>
</ul>
</li>
</ul>
<form class="d-flex mt-3" role="search">
<input class="form-control me-2" type="search" placeholder="Search" aria-label="Search">
<button class="btn btn-success" type="submit">Search</button>
</form>
</div>
</div>
</div>
</nav>
</header>
<main>
<h1>Hello world!</h1>
</main>
<script src="https://cdn.jsdelivr.net/npm/bootstrap@5.3.0/dist/js/bootstrap.bundle.min.js" integrity="sha384-geWF76RCwLtnZ8qwWowPQNguL3RmwHVBC9FhGdlKrxdiJJigb/j/68SIy3Te4Bkz" crossorigin="anonymous"></script>
</body>
</html>
вот так выглядит полученная страница
и каким то образом, весь тег body попадает под этот навбар, т.е все остальное на странице как бы появляется, но закрывается этим навбаром.
Средний
