diff --git a/devtools/client/responsive.html/index.css b/devtools/client/responsive.html/index.css
index 509d4d10396..7e78f734a6d 100644
--- a/devtools/client/responsive.html/index.css
+++ b/devtools/client/responsive.html/index.css
@@ -197,6 +197,6 @@ body {
   text-align: center;
 }
 
-.viewport-dimension-span {
+.viewport-dimension-separator {
   -moz-user-select: none;
 }