fix flex-tab on cordova

packages/rocketchat-theme/client/imports/base.less

@@ -4432,6 +4432,8 @@ body:not(.is-cordova) {
 		position: absolute;
 		width: 100%;
 		height: 100%;
+		top: 0;
+		left: 0;
 
 		.flex-tab {
 			position: relative;