diff --git a/assets/herman.css b/assets/herman.css
index e2dfc11..9bf7f0c 100644
--- a/assets/herman.css
+++ b/assets/herman.css
@@ -245,3 +245,13 @@ figcaption > p {
   text-align: center;
   font-style: italic;
 }
+
+#heatmap-caption {
+  color: #888;
+}
+
+@media (prefers-color-scheme: light) {
+  #heatmap-caption {
+    color: #3d4449;
+  }
+}