Remove extra margin from warning messages in authenticate page

In the public share authentication page the form elements appear inside
a container that uses the "warning" CSS class. When the given password
is wrong a warning message is shown inside that container; this message
uses the "warning" CSS class too, so the top margin set for ".warning"
elements need to be removed in that case.

Signed-off-by: Daniel Calviño Sánchez <danxuliu@gmail.com>

core/css/publicshareauth.css

@@ -26,3 +26,8 @@ input[type='submit'].icon-confirm {
 	height: 45px;
 	background-color: transparent !important;
 }
+
+.warning > .warning {
+	/* Do not use a top margin for warning messages in the warning container. */
+	margin-top: 0;
+}