fixup! Bug 40925: Implemented the Security Level component

Use --warning-color variable for the Custom label in the security level popup.


(cherry picked from commit 4f7b3857)

browser/components/securitylevel/content/securityLevelPanel.css

@@ -49,7 +49,7 @@
 
 #securityLevel-custom {
   border-radius: 4px;
-  background-color: var(--yellow-50);
+  background-color: var(--warning-color);
   color: black;
   padding: 0.4em 0.5em;
   margin-inline-start: 1em;