diff --git a/doc/style.css b/doc/style.css
index 7549ee2e1145..96b6979474db 100644
--- a/doc/style.css
+++ b/doc/style.css
@@ -325,8 +325,10 @@ div.appendix .important > :last-child {
 
 div.book .note,
 div.book .tip,
+div.book .important,
 div.appendix .note,
-div.appendix .tip {
+div.appendix .tip,
+div.appendix .important {
   color: var(--note-text-color);
   background: var(--note-background);
 }