sticky footer not working bootstrap

1
2/* 2020 - bootstrap 4.5+ 
3Note: - The flex-fill utility was included in Bootstrap 4.1 at later release. 
4So after that release the extra CSS for flex-fill won't be needed. 
5Additionally min-vh-100 is included in newer Bootstrap 4 releases */
6<div class="d-flex flex-column min-vh-100">
7    <nav>
8    </nav>
9    <main class="flex-fill">
10    </main>
11    <footer>
12    </footer>
13</div>
14