Why footer isn't sticking with bottom?after reducing the width of the window?

Question

Why footer isn't sticking with bottom after reducing the width of the window?

<footer>
copyright
</footer>

Code: https://codepen.io/FilipoV/pen/rNjgOoW

Answer 1

If you mean that it get's some space under the footer after reducing window and then scrolling, a fix is:

body {
min-height: 100vh;}