LibWeb: Add rudimentary styling to <details> and <summary>

Author: https://github.com/AtkinsSJ
Commit: 2f3e24d71e
Pull-request: https://github.com/SerenityOS/serenity/pull/11382
Reviewed-by: https://github.com/davidot ✅

Userland/Libraries/LibWeb/CSS/Default.css

@@ -233,3 +233,13 @@ input[type=text] {
 option {
     display: none;
 }
+
+details {
+    display: block;
+    padding-left: 1em;
+}
+
+summary {
+    display: block;
+    font-weight: bold;
+}