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Go to Settings -> Lister Themes and then File -> Import Theme and find the .dlt file you downloaded. If the thing you downloaded isn't a .dlt file (or a .dlt file inside a zip archive) then it's probably just an a background image or some icons and will need to be configured manually using Preferences/Images or Customize.
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Watch this video (doesn't require sound): [Toolbar Editing (video tutorial)) and, once you're familiar with all of that, you can drag & drop applications to the toolbar while in Customize mode.
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See this recent thread: [Single window mode?)