Remove experimental ::details-summary pseudo-element.

Developers can already style the <summary> element.  Being able to style
a pseudo-element that wraps only the <summary> element has little value
and appears to add substantial confusion.  (It does slightly improve the
ability to style the default summary when no summary is provided, but
not necessarily in useful ways.)

Bug: 1469418
Change-Id: Ia0c9bfd61696e5ca46e4ab3113e7bc45fde88bf4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5137042
Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Auto-Submit: David Baron <dbaron@chromium.org>
Commit-Queue: David Baron <dbaron@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1239642}
diff --git a/html/rendering/the-details-element/details-pseudo-elements-001-ref.html b/html/rendering/the-details-element/details-pseudo-elements-001-ref.html
index 43f2216..e00e6c5 100644
--- a/html/rendering/the-details-element/details-pseudo-elements-001-ref.html
+++ b/html/rendering/the-details-element/details-pseudo-elements-001-ref.html
@@ -4,7 +4,6 @@
 <style>
 
 div { background: aqua }
-summary { background: fuchsia }
 
 </style>
 
diff --git a/html/rendering/the-details-element/details-pseudo-elements-001.tentative.html b/html/rendering/the-details-element/details-pseudo-elements-001.tentative.html
index 0832197..1a9f7d6 100644
--- a/html/rendering/the-details-element/details-pseudo-elements-001.tentative.html
+++ b/html/rendering/the-details-element/details-pseudo-elements-001.tentative.html
@@ -10,10 +10,6 @@
   background: aqua;
   display: block; /* override display: contents for slot */
 }
-details::details-summary {
-  background: fuchsia;
-  display: block; /* override display: contents for slot */
-}
 
 </style>