Permit nested admonitions

Use the documentations' language to nudge users away from doing this.

docs/reference/admonitions.md

@@ -134,3 +134,43 @@ Maaa! I made it look the same by setting the class.
 ```{todo}
 Describe the CSS variables needed.
 ```
+
+## Nesting admonitions
+
+
+``````{furo-demo}
+`````{note}
+You can nest admonitions.
+
+````{warning}
+But you really should not.
+
+```{danger}
+It's distracting.
+```
+
+And can be confusing for the user to understand.
+````
+
+And, honestly, looks weird.
+`````
+
++++
+
+.. note::
+
+   You can nest admonitions.
+
+   .. warning::
+
+      But you really should not.
+
+      .. danger::
+
+         It's distracting.
+
+      And can be confusing for the user to understand.
+
+   And, honestly, looks weird.
+
+``````

src/furo/assets/styles/content/_admonitions.sass

@@ -54,11 +54,11 @@
   @each $type, $value in $admonitions
     &.#{$type}
       border-left-color: var(--color-admonition-title--#{$type})
-      .admonition-title
+      > .admonition-title
         background-color: var(--color-admonition-title-background--#{$type})
         &::before
           background-color: var(--color-admonition-title--#{$type})
           mask-image: var(--icon-#{nth($value, 2)})
 
-.admonition-todo .admonition-title
+.admonition-todo > .admonition-title
   text-transform: uppercase

src/furo/sphinxext.py

@@ -39,12 +39,12 @@ def _md_demo(block: str) -> StringList:
     if not block.strip("\n"):
         return StringList()
 
-    lines.append("`````{tab} Markdown (MyST)")
-    lines.append("````md")
+    lines.append("````````{tab} Markdown (MyST)")
+    lines.append("```````md")
     lines.extend(block.splitlines())
-    lines.append("````")
+    lines.append("```````")
     lines.extend(block.splitlines())
-    lines.append("`````")
+    lines.append("````````")
 
     return StringList(lines)
 
@@ -54,15 +54,15 @@ def _rst_demo(block: str) -> StringList:
     if not block.strip():
         return StringList()
 
-    lines.append("`````{tab} reStructuredText")
-    lines.append("````{eval-rst}")
+    lines.append("````````{tab} reStructuredText")
+    lines.append("```````{eval-rst}")
     lines.append(".. code-block:: rest")
     lines.append("")
     lines.extend(indent(block, "    ").splitlines())
     lines.append("")
     lines.extend(block.splitlines())
-    lines.append("````")
-    lines.append("`````")
+    lines.append("```````")
+    lines.append("````````")
 
     return StringList(lines)