Fix Navigation menu shadow and added rules for icon in button

Signed-off-by: John Molakvoæ (skjnldsv) <skjnldsv@protonmail.com>

core/css/apps.scss

@@ -620,6 +620,7 @@ em {
 			height: auto;
 			margin: 0;
 			font-weight: inherit;
+			box-shadow: none;
 			/* prevent .action class to break the design */
 			&.action {
 				padding: inherit !important;

core/css/inputs.scss

@@ -140,6 +140,7 @@ button, .button {
 		&[class*=' icon-'] {
 			display: inline-block;
 			vertical-align: text-bottom;
+			opacity: 0.5;
 		}
 	}
 }