title: Have one way to toggle a site-wide message
body: <p>I want to have a site-wide message that can be toggled in a single place. On the <code>&lt;front&gt;</code> page, this site will appear in one location in the UI. On every other page, it will appear in a different location.</p>
  
  <p>Here's the approach I've come up with:</p>
  
  <ol>
  <li>In "Custon Block Library" (<code>/admin/structure/block/block-content</code>), create a custom block with the right content </li>
  <li>In "Block Layout" (<code>/admin/structure/block</code>), add the block to both places I want it to appear.</li>
  </ol>
  
  <p>To show the alert message:</p>
  
  <ol>
  <li>Set the front page block to show on <code>&lt;front&gt;</code></li>
  <li>Set the other page block to hide on <code>&lt;front&gt;</code></li>
  </ol>
  
  <p>To hide the alert message:</p>
  
  <ol>
  <li>Set both blocks to hide on <code>*</code></li>
  </ol>
  
  <p>This seems like it will work, but I'd rather have a single place to toggle the message. Is it possible to say "site-wide, I want to hide / show this block"? Or are blocks the wrong solution for this?</p>