duplicate IDs

I am updating an old site to, among other things, make it responsive. The site uses a sidebar for navigation. The navigation menu uses IDs to tell the site visitors where they are within the site (the current page's link is a different color). For smaller browser windows, the sidebar disappears and is replaced by navigation menus above and below the content. Here's the rub: since the IDs are doing the same thing, and since only one set of IDs is visible for any window size, it seems...

duplicate IDs

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