Menu Bar Glitch When Scrolling

I have another question based off of this thread:

“Hello karagol,

Hope you’re well! 🙂

First of all, use child themes for any customization you will make. Read more about it here: http://codex.wordpress.org/Child_Themes

Do you want something like this http://prntscr.com/5p6jhs ? If so, create a file inside your child theme’s folder named header.php then paste the code found on the link below:

https://gist.github.com/anonymous/a840cbf4020cef57bc79

Let me know if that helps! 🙂

Take care,
Calvin”

My site is http://www.mountaintopsoftware.com When scrolling, for example on the Front Page, the menu bar goes from full width to half width and it creates a jumpy-like glitch. Is there a way to keep my menu nav bar static full width on the top of all of my pages? Thank you in advance for your response.