FIX: revert inadvertently removed css class (#9360)

FIX: revert inadvertently removed css class (#9360)

diff --git a/app/assets/javascripts/discourse/templates/user/messages.hbs b/app/assets/javascripts/discourse/templates/user/messages.hbs
index 643928f..3dc34f6 100644
--- a/app/assets/javascripts/discourse/templates/user/messages.hbs
+++ b/app/assets/javascripts/discourse/templates/user/messages.hbs
@@ -1,7 +1,7 @@
 {{#d-section class="user-secondary-navigation" pageClass="user-messages"}}
   {{#unless site.mobileView}}
     {{#if showNewPM}}
-      {{d-button class="btn-primary new-" action=(route-action "composePrivateMessage") icon="envelope" label="user.new_private_message"}}
+      {{d-button class="btn-primary new-private-message" action=(route-action "composePrivateMessage") icon="envelope" label="user.new_private_message"}}
     {{/if}}
   {{/unless}}
 
@@ -72,7 +72,7 @@
     {{#if site.mobileView}}
       {{#if showNewPM}}
         {{d-button
-          class="btn-primary new-"
+          class="btn-primary new-private-message"
           action=(route-action "composePrivateMessage")
           icon="envelope"
           label="user.new_private_message"}}

GitHub sha: 028915e4

This commit appears in #9360 which was merged by jjaffeux.