diff --git a/public/css/theme-arc-red.css b/public/css/theme-arc-red.css
index eaff6d9..6e9c8cb 100644
--- a/public/css/theme-arc-red.css
+++ b/public/css/theme-arc-red.css
@@ -264,7 +264,7 @@ span.green .svg {
 /* not needed: .repository .diff-detail-box */
 
 details {
-    background-color: var(--color-secondary-light-4); /* make collapsible elements easier to distinguish from main body */
+    background-color: var(--color-secondary-light-3); /* make collapsible elements easier to distinguish from main body */
     border-radius: 4px; /* same as code blocks */
     padding: .2em .4em; /* same as code blocks */
 }
diff --git a/public/css/theme-auto-red.css b/public/css/theme-auto-red.css
index 3022c48..e9485ce 100644
--- a/public/css/theme-auto-red.css
+++ b/public/css/theme-auto-red.css
@@ -362,7 +362,7 @@
     /* not needed: .repository .diff-detail-box */
 
     details {
-        background-color: var(--color-secondary-light-4); /* make collapsible elements easier to distinguish from main body */
+        background-color: var(--color-secondary-light-3); /* make collapsible elements easier to distinguish from main body */
         border-radius: 4px; /* same as code blocks */
         padding: .2em .4em; /* same as code blocks */
     }