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If you're editing content, you must have opened an existing Alert.
A finished site-wide alert looks like this:
A site-wide alert is displayed at the top of all screens and used to share urgent information. You can have it so that it always shows up every time the person comes onto the site, or you can have it dismissible which gives the people an option to dismiss it once they’ve seen it.
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Site-Wide – this is if you want the alert to show up on every page of the site and it isn’t only about one specific part of the web.
An in-page alert is displayed at the top of a specific page that you wish the alert to be placed on and only relevant to that page.
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