Bug 1860214 - Tweak the certificate deletion dialog to not push dialog buttons out of view. r=emilio

Maybe there's a better way to get the dialog to flex for long richlistbox's,
but this seemed simplest. I'm open to other suggestions.

Differential Revision: https://phabricator.services.mozilla.com/D194938

security/manager/pki/resources/content/deletecert.css

@@ -12,8 +12,13 @@ dialog::part(content-box) {
   contain: inline-size;
 }
 
+#impact {
+  margin-block-start: 12px;
+}
+
 #certlist {
   flex: 1;
   min-height: 8em;
+  contain: size;
   min-width: 35em;
 }