diff --git a/static/css/theme.css b/static/css/theme.css
index 206612f950..68ecc58df7 100644
--- a/static/css/theme.css
+++ b/static/css/theme.css
@@ -2241,7 +2241,7 @@ html[dir="rtl"] #R-sidebar ul.collapsible-menu > li > label > i.fa-chevron-right
     display: none;
     /* if setting a border to 1px, a browser instead sets it to 1dppx which is not
     usable as a unit yet, so we have to calculate it ourself */
-    margin-top: calc( -1px / var(--bpx) );
+    margin-top: calc( var(--bpx1)*-1px );
     z-index: 10;
 }