====== Creating a Responsive Sidebar ======

<code>
<div class="d-flex">
    <nav class="nav flex-column bg-light p-3" style="width: 250px;">
        <a class="nav-link" href="#introduction">Introduction</a>
        <a class="nav-link" href="#chapter1">Chapter 1</a>
        <a class="nav-link" href="#chapter2">Chapter 2</a>
    </nav>
    <div class="content flex-grow-1 p-3">
        <h2>Welcome to the Book</h2>
        <p>Content goes here...</p>
    </div>
</div>
</code>