styles: add alert styles into shadow dom

rhodecode/public/css/polymer.less

@@ -1,23 +1,24 b''
 //Primary CSS
 //--- IMPORTS ------------------//
 @import 'helpers';
 @import 'mixins';
 @import 'variables';
 @import 'buttons';
+@import 'alerts';
 
 :root {
     --primary-color: @rcblue;
     --light-primary-color: @rclightblue;
     --dark-primary-color: @rcdarkblue;
     --primary-text-color: @text-color;
 
     --paper-spinner-layer-1-color: @grey6;
     --paper-spinner-layer-2-color: @grey5;
     --paper-spinner-layer-3-color: @grey4;
     --paper-spinner-layer-4-color: @grey3;
 }
 
 .paper-toggle-button {
   display: inline;
 }