diff --git a/dencoder.css b/dencoder.css
index 32677a7..a496586 100644
--- a/dencoder.css
+++ b/dencoder.css
@@ -27,6 +27,16 @@ textarea.input {
 	width: -moz-available;
 }
 
+textarea.input.error {
+	background-color: #f88;
+	border-color: #f00;
+}
+
+textarea.input.error:focus, textarea.input.error:hover {
+	background-color: #faa;
+	border-color: #f00;
+}
+
 select.conversion {
 	border-radius: 0.2em;
 	border-style: solid;