Can you describe a bit what are you trying to accomplish? I believe there is some misunderstanding here, since the CSS provided does make your NavBar transparent but since the content element is below it and has overflow: hidden, it won't be visible under the NavBar when you scroll. Maybe you want all the scrolling content to pass under the NavBar? Then you need to remove the overflow: hidden from .km-content and move the background to the .km-scroll-container.
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