diff --git a/web_src/css/form.css b/web_src/css/form.css
index 916d76fd0c..8b15e5fd7c 100644
--- a/web_src/css/form.css
+++ b/web_src/css/form.css
@@ -334,6 +334,10 @@ input:-webkit-autofill:active,
   display: inline-block;
 }
 
+.captcha-img {
+  width: min(30em, 100%);
+}
+
 @media (min-width: 768px) {
   .g-recaptcha-style,
   .h-captcha-style {
diff --git a/web_src/css/markup/dark.css b/web_src/css/markup/dark.css
index 700a48518e..7c8e633c74 100644
--- a/web_src/css/markup/dark.css
+++ b/web_src/css/markup/dark.css
@@ -11,3 +11,10 @@
 .markup [href$="#dark-mode-only"] {
   display: unset;
 }
+
+
+/* The reason we're doing this *here* is because dark vanilla templates always use this file, and there's no other way to detect dark theme */
+
+.captcha-img {
+  filter: invert();
+}