diff --git a/_static/css/custom.css b/_static/css/custom.css
index 9ddf21e67..7764b8aae 100644
--- a/_static/css/custom.css
+++ b/_static/css/custom.css
@@ -544,6 +544,11 @@ code,
 
 /* Syntax highlighting */
 
+/* Remove default red boxes around Pygments errors */
+.highlight .err {
+    border: none;
+}
+
 .highlight {
     background-color: var(--highlight-background-color);
 }