No sticky navigation menu

Problem/Motivation

While going through the theme for issues I found out that the navigation is not sticky. Attaching the screen recording for a better understanding and making the issue clearer.

Steps to reproduce

Install the theme
Add 10-20 articles and check for the pagination.
Scroll a bit and you will notice that navigation doesn't stick to the top.

Proposed resolution

Make navigation menu sticky.

Remaining tasks

none

User interface changes

Yes

API changes

none

Data model changes

none