diff --git a/css/derekovecs.css b/css/derekovecs.css
index 82a7eda..3a1c6db 100644
--- a/css/derekovecs.css
+++ b/css/derekovecs.css
@@ -234,6 +234,27 @@
     overflow: hidden; /* will contain if #first is longer than #second */
 }
 
+/* Explains, in the place of a table, why that table has nothing to show. */
+.notice {
+    align-self: flex-start;
+    max-width: 40em;
+    padding: 8px 12px;
+    color: #555;
+    border-left: 3px solid #ccc;
+    background-color: #fafafa;
+}
+
+/* Query operands that are not in the vocabulary. The result is computed
+   without them, so this has to be visible next to it. */
+#unknownwords {
+    width: 800px;
+    margin: 0 auto 10px auto;
+    padding: 4px 8px;
+    border-left: 3px solid #c00;
+    background-color: #fff4f4;
+    box-sizing: border-box;
+}
+
 #topwrapper {
     width: 100%;
     display: flex;