do not change input's colors in dark mode (#3769)

Hardcode transparent background and black text color for inputs.
Otherwise, the inputs end up with dark background and white text
which does not work with the rest of the dialog that always has white
background.
This is temporary until the rest of the dialog works with the dark mode.

Fixes: #3768

chrome/skin/default/zotero/integration.css

@@ -117,6 +117,9 @@
 	box-sizing: border-box; 
 	height: 15px;
 	margin: 0;
+	/* Keep the background and text color unchanged in dark mode */
+	background-color: transparent;
+	color: black;
 }
 
 .citation-dialog span {