Just wanted to share a solution to those looking for a fixed header menu. This type of fixed header stretches from side to side but keeps the content/menu elements centered within your page. Here's an example of the end result:
First drop a 'box' widget near the top of your page section. Give it the appropriate height and drag out the width to touch side to side of your page guides. Apply your intended styling to it's background properties.
Next drop in any other widgets or content within the box. Make sure everything is positioned and kept within the borders of your page guides.
Replace the box ID with your own boxes ID:
You can find your boxes ID by clicking on the box and referring to the bottom of the 'Properties' menu.
That's about it! Now hit preview and see your results.
If you have any questions or run into any issues reply below or shoot an email over to firstname.lastname@example.org