This is an OceanWP Pro plugin.  It is designed to create sticky headers that stay at the top of the page when you scroll up and down. 

I clicked on the section for the menu in the header.  I added to CSS Classes: owp-sticky.  This works with OceanWP Sticky Header in keeping only the menu at the top of the page when scrolling.

First picture is how you set the menu.  I have 20+ menus.  The second picture is what I used to set the typography for the menu.  The third picture is setting the background color to black.