It appears that some of you noticed the disappearance of the downloads icon with the latest Steam update. For some unknown reason, Valve decided to change the z-position value of the downloads section so it now renders behind the main content of the client. Unfortunately, zpos is a hard-coded value that skins can't change which means the previous material styled icon is no longer possible.
All of that said, the downloads icon has been re-situated to the top bar, which is the only place it can now be visible without adding a bottom bar to the skin.
Please keep in mind that the new chat UI is not skinnable. See this post for more details.