Add standard border-radius to datepicker

Signed-off-by: Jan-Christoph Borchardt <hey@jancborchardt.net>

core/css/styles.scss

@@ -992,6 +992,8 @@ code {
 	margin-top: 10px;
 	padding: 4px 8px;
 	width: auto;
+	border-radius: 3px;
+	border: none;
 
 	.ui-state-default,
 	.ui-widget-content .ui-state-default,