Add mixin to inherit from icon classes

app/assets/fonts/openproject_icon/openproject-icon-font.template.scss

@@ -5,6 +5,9 @@
 }
 
 {{#each codepoints}}
+@mixin icon-mixin-{{@key}} {
+    content: "\\{{this}}";
+}
 .{{../classPrefix}}{{@key}}:before {
 	content: "\\{{this}}";
 }

app/assets/stylesheets/fonts/_openproject_icon_font.sass

@@ -225,7 +225,6 @@
 
 .icon-work_package-edit
   @extend .icon-ticket-edit
-  content: "\f1a7"
 
 .icon-work_package-note
   @extend .icon-ticket-note

app/assets/stylesheets/layout/_main_menu_mobile.sass

@@ -33,8 +33,11 @@
   #main-menu
     position: absolute !important
     height: initial !important
-    overflow: auto !important
+    overflow: auto
     z-index: 11
 
+  .hidden-navigation #main-menu
+    overflow: hidden
+
   .main-item-wrapper a
     width: 100%

app/assets/stylesheets/layout/_top_menu_mobile.sass

@@ -76,7 +76,7 @@
           text-align: center
 
           &:not(.login):before
-            content: "\f1d7" !important
+            @include icon-mixin-user
             padding: 0.25rem
             @include icon-font-common