(css) Fix close button of card and msg viewers

UI/Templates/ContactsUI/UIxContactViewTemplate.wox

@@ -9,7 +9,7 @@
     <div class="sg-face" layout="column" layout-fill="layout-fill">
       <md-card>
         <md-card-actions flex-none="flex-none" layout="row" layout-align="end center">
-          <md-button class="sg-icon-button show hide-gt-md"
+          <md-button class="sg-icon-button hide-gt-xs"
                      label:aria-label="Close"
                      ng-click="editor.close()">
             <md-icon>close</md-icon>

UI/Templates/MailerUI/UIxMailViewTemplate.wox

@@ -17,7 +17,7 @@
                      ng-click="viewer.closePopup()">
             <md-icon>close</md-icon>
           </md-button>
-          <md-button class="md-icon-button hide-gt-md"
+          <md-button class="md-icon-button hide-gt-xs"
                      ng-hide="isPopup"
                      label:aria-label="Close"
                      ng-click="viewer.close()">