Issue U4-5307 - Added umb-editor css class to allow text box stretching.

src/Umbraco.Web.UI.Client/src/views/propertyeditors/multipletextbox/multipletextbox.html

@@ -1,7 +1,7 @@
 <div class="umb-editor umb-multiple-textbox" ng-controller="Umbraco.PropertyEditors.MultipleTextBoxController">
 
     <div class="control-group" ng-repeat="item in model.value">
-        <input type="text" name="item_{{$index}}" ng-model="item.value" />
+        <input type="text" name="item_{{$index}}" ng-model="item.value" class="umb-editor" />
         <a prevent-default href="" title="Remove this text box"
             ng-show="model.value.length > model.config.min"
             ng-click="remove($index)">