diff --git a/apps/client/src/stylesheets/theme-next/shell.css b/apps/client/src/stylesheets/theme-next/shell.css
index 880e85f70..e84c4544d 100644
--- a/apps/client/src/stylesheets/theme-next/shell.css
+++ b/apps/client/src/stylesheets/theme-next/shell.css
@@ -64,6 +64,7 @@ body.background-effects.theme-supports-background-effects.platform-win32.layout-
 
 body.background-effects.theme-supports-background-effects.platform-win32.layout-horizontal {
     --center-pane-background-color-bgfx: var(--center-pane-horiz-layout-background-color-bgfx);
+    --gutter-color: var(--left-pane-background-color);
 }
 
 body.background-effects.theme-supports-background-effects.platform-win32,