diff --git a/forum/extension/less/embed.less b/forum/extension/less/embed.less
index 90581efb..51f61a03 100644
--- a/forum/extension/less/embed.less
+++ b/forum/extension/less/embed.less
@@ -7,3 +7,7 @@ body, .App { background: @oc-panel; }
 .Page-content { max-width: none; }
 .Post-body a, .PostUser-name a, .Button--link { color: @oc-accent; }
 .Button--primary { background: @oc-accent; }
+// The reply box follows the page while scrolling; the forum paints it in its header colour
+// (dark when a coloured header is configured), which reads as a black block here.
+.DiscussionPage-nav > ul { background: @oc-panel; }
+.DiscussionPage-nav .item-scrubber, .DiscussionPage-nav a { color: inherit; }