Fix blockquote.warning styles in documentation

Change-Id: Ic5362488e84553996afa4c3fc7baee9632f7af77
diff --git a/dev/scss/base/base.scss b/dev/scss/base/base.scss
index ebd80e7..2ad7b95 100644
--- a/dev/scss/base/base.scss
+++ b/dev/scss/base/base.scss
@@ -91,7 +91,8 @@
   mix-blend-mode:   soft-light;
 
   &.bug,
-  &.missing {
+  &.missing,
+  &.warning {
     border-left-color: $dark-red;
     background-color:  $middle-red;
     color:             $nearly-white;