diff --git a/wagtail/wagtailadmin/static/wagtailadmin/scss/core.scss b/wagtail/wagtailadmin/static/wagtailadmin/scss/core.scss
index e55bc23ca..05a24082e 100644
--- a/wagtail/wagtailadmin/static/wagtailadmin/scss/core.scss
+++ b/wagtail/wagtailadmin/static/wagtailadmin/scss/core.scss
@@ -850,7 +850,7 @@ footer, .logo{
         }
     }
     .explorer {
-        z-index:@explorer-z-index;
+        z-index:$explorer-z-index;
     }
     .nav-wrapper{
         z-index:auto; /* allows overspill of messages banner onto left menu, but also explorer to spill over main content */
diff --git a/wagtail/wagtailadmin/static/wagtailadmin/scss/mixins.scss b/wagtail/wagtailadmin/static/wagtailadmin/scss/mixins.scss
index b4cb42618..05d23455d 100644
--- a/wagtail/wagtailadmin/static/wagtailadmin/scss/mixins.scss
+++ b/wagtail/wagtailadmin/static/wagtailadmin/scss/mixins.scss
@@ -80,6 +80,9 @@
         width: auto; 
     }
 }
+.visuallyhidden{
+    @include visuallyhidden;
+}
 
 @mixin visuallyvisible{
     clip:none;
@@ -88,4 +91,8 @@
     margin:auto;
     overflow:visible;
     position:initial;
+}
+
+.visuallyvisible{
+    @include visuallyvisible;
 }
\ No newline at end of file