Add deprecated admonition

docs/handbook/meta/syntax.md

@@ -96,6 +96,21 @@ Here are some common admonitions, when you might use them, and quick code snippe
 ### Custom
 We've modified a couple of the standard admonitions to mean something a little different on this site.
 
+#### Deprecated
+For pages that were once accurate, but are either no longer accurate and not being updated, or have become obsolete due to discontinuation, etc.
+
+!!! deprecated "Deprecated"
+    The `deprecated` admonition looks like this.
+
+??? quote "Syntax"
+    Copy and paste at the top of page content:
+    ```
+    !!! deprecated "Deprecated"
+        The contents of this page are deprecated. Do not rely on any information on this page to be accurate, as it is not being updated.
+
+        Please see <insert page link, if available> for the equivalet updated information.
+    ```
+
 #### Work in Progress
 For pages that aren't yet complete, and need revisions (that we know are going to be revised sooner/more frequently than a typical page.)
 

docs/stylesheets/extra.css

@@ -1,3 +1,21 @@
+:root {
+  --md-admonition-icon--deprecated: url('data:image/svg+xml;charset=utf-8,<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><path d="M10 2h4c3.31 0 5 2.69 5 6v10.66C16.88 17.63 15.07 17 12 17s-4.88.63-7 1.66V8c0-3.31 1.69-6 5-6M8 8v1.5h8V8zm1 4v1.5h6V12zM3 22v-.69c2.66-1.69 10.23-5.47 18-.06V22z"/></svg>')
+}
+.md-typeset .admonition.deprecated,
+.md-typeset details.deprecated {
+  border-color: rgb(98, 114, 164);
+}
+.md-typeset .deprecated > .admonition-title,
+.md-typeset .deprecated > summary {
+  background-color: rgba(98, 114, 164, 0.1);
+}
+.md-typeset .deprecated > .admonition-title::before,
+.md-typeset .deprecated > summary::before {
+  background-color: rgb(98, 114, 164);
+  -webkit-mask-image: var(--md-admonition-icon--deprecated);
+          mask-image: var(--md-admonition-icon--deprecated);
+}
+
 .note-blue {
     color: #448AFF;
   }