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.