To start, navigate to your Layout that contains the menu you would like to turn into a fixed menu.
Next click on the "Customize Design" (Paintbrush) icon and paste the following in the CSS > Additional CSS section as shown in the image below
overflow: inherit; position: fixed; top: 0; left:0; width: 100%; z-index:1049;
Next, we'll need to add the following one line of CSS to the same part of the Page Container as shown in the image below.
That is all! As we can see our header is now fixed at the top as you scroll down on the page.