Two small improvements:

Fix oversight duplicate property left in CSS (dark theme).

Improve wording in comment that mentions `appearance: none`

src/librustdoc/html/static/css/rustdoc.css

@@ -984,8 +984,8 @@ table,
 	text-indent: 0.01px;
 	background-color: var(--main-background-color);
 }
-/* cancel stylistic differences in padding
-in firefox for "appearance: none" <select>s */
+/* cancel stylistic differences in padding in firefox
+for "appearance: none"-style (or equivalent) <select>s */
 @-moz-document url-prefix() {
 	#crate-search {
 		padding-left: 0px; /* == 4px - 4px */