Ticket #26630: 26630.4.patch

src/wp-admin/css/admin-menu.css

@@ -348 +348 @@
         padding: 7px 0;
         -webkit-transition: all .1s ease-in-out;
         transition: all .1s ease-in-out;
+
+        /* Copy from .dashicons-before:before for back compat */
+        display: inline-block;
+        width: 20px;
+        height: 20px;
+        font-size: 20px;
+        line-height: 1;
+        font-family: "dashicons";
+        text-decoration: inherit;
+        font-weight: normal;
+        font-style: normal;
+        vertical-align: top;
+        text-align: center;
+        -webkit-font-smoothing: antialiased;
+        -moz-osx-font-smoothing: grayscale;
 }
 
 #adminmenu div.wp-menu-image:before {